An endless stream of random encounters

The forest of Arboreal Trees

The players come upon an area of land that has been turned into a brown acidic mush, while strange alien looking trees slowly consume the land. The trees look like tall fleshy, red structures. But instead of branches or a canopy, the Arboreal Tree has a couple of red leafs at the top, crowned by a cluster of strange purple fruit. Any land these trees touch slowly turns into the same goo. The trees move about 5 foot per hour, but over the course of a few days they can slowly cover quite a bit of distance. The alien fruit is poisonous, and the trees can be destroyed with sharp magical weapons, or fire.

With a successful DC 16 wisdom (survival) check the players can locate the origin of the alien trees: a crashed alien spaceship, shaped like a giant metal wood-louse. Hostile other-worldy monsters may be nearby and attack the players. The cargo area of the ship is broken, spilling many of the purple fruit on the land, and thus spreading the infection.

The subterranean portal

The players encounter a small stream flowing from a cave. Upon exploring the cave, they find a bright purple portal from which the stream is flowing. The portal leads to another land location elsewhere in the world, where water simply flows into the portal. The portal may have been caused by some magical incident, or it may be a natural phenomenon.

The sunken cathedral

The players find the ruins of an ancient cathedral. The cathedral is flooded with water, because it has sunken partially into a lake or swamp. The roof is missing, and the cathedral may be inhabited by hostile monsters. If the cathedral is still in use, then there willl be signs of this in the form of lit candles, which are much newer than the building. In the main hall of the cathedral is a large statue dedicated to some ancient god. If there are hostile creatures in the cathedral, they may be worshipping the god. As the players explore the building, the water in the cathedral reaches up to their knees in many places, and up to their waist in others. This slows the movement of the players down.

The lazy dragon

The players encounter a group of farmers who have just been attacked by a dragon. The dragon took some of their cattle as they were on their way to the market. The farmers ask the players to deal with the dragon, but surprisingly none of the farmers seems injured.

The players can find the dragon at its cave, feasting on a couple of cows, while lying on a pile of junk. The dragon is fat, and none of its hoard are of any value. It pays the players no mind, and they can take what ever they like, since nothing in the cave is of any real value. It will only fight the players if they really insist. The dragon speaks common, and is very content with what little he has to do to stay fed. A banquette of cattle is paraded to town every week, which provides him with food without much effort.

The dragon holds a princess hostage, but it turns out the princess willingly kidnapped herself, to avoid being married to a prince she does not like. The dragon doesn't want the princess in his lair, but he is also too lazy to drive her away. The king does not bother with sending someone after her, because he sees through her trick, and expects she'll return home eventually.

As long as the players don't attack the dragon, he is friendly to them.

The arctic asteroid

A large asteroid has crashed down onto this part of the land, changing the climate of a very local area surrounding the asteroid to a cold climate. The asteroid itself is about the size of a cathedral, and is partially made of rock and ice. The players may encounter ice elementals here, or other creatures that fit a cold climate. If the players take a sample of the asteroid, this could be valuable to a blacksmith or wizard.

The automaton arena

A wizard is organizing a tournament in town. He has an automaton that will fight contestants, and whoever succeeds in defeating the automaton, can win a lot of gold. The automaton regenerates automatically between each fight, so that every contestant fights him at full HP. Only one combatant is allowed to fight him at a time. Once a combatant surrenders, or is down to 0 HP, the automaton automatically stops fighting, so the contestant can be carted off to the hospital. Many knights in shiny armor (mostly noble men) have lined up to have a go. If the automaton takes electricity damage, it goes rogue and will attack anyone (including the audience).

The forest of the fallen army

This forest is full of giant stone soldiers that are scattered about, and overgrown with plants and a thick layer of moss. Every statue is in a different pose, as if it slouched down after a long battle. Each statue wears a stone suit of armor, and carries its own stone weaponry. It seems the stone army has been lying motionless in this forest for so long, that neither the locals, nor animals, pay any attention to them. The army must have been here for ages, because nature has adapted to their presence, and some of the statues are partially swallowed by the trees. The forest seems to have grown around them.

The Roadside Fortuneteller
A woman has setup her fortunetelling stand along a well traveled road near the edge of a village or small town - tea leaves, tarot, palm reading, or what have you. If the characters visit her, her predictions could be based on past, present or future events with varying accuracy. Useful for seeding future plot hooks or perhaps steering the party back on course.

Should they feel the need to investigate her, the party finds out that she is an integral part of the community - making charms and wards and some talents as a healer, though she isn't related to anyone nearby and no one remembers when she moved to the area.

Tastes Like Chicken!
A curious looking butcher is pushing his cart to market as the party is heading out of town. He hails the party and offers them a deal. They are obviously equipped for some time in the wilderness - they should buy some of his fresh meat for one last meal tonight before resorting to rations and what they can forage. The meat is dark in color and he has some pre-cooked samples to try if they wish. It is rather tasty (Prestidigitation), despite its odd appearance. What he is selling is troll steaks, but it will be hours before they regenerate enough to become a problem.

The unethical attraction
A traveling showman exploits a caged orc as an attraction. He travels from town to town, showing the beast in all its fury, and allows children to pelt it with rotten fruit. The orc desperately wants to be freed from the cage, and can speak a little bit of common (something it taught itself over the years of abuse). The players can deduce from the look in the eyes of the orc that he is deeply unhappy, but they won't be given an opportunity to talk to the orc during the day. At night the cage is covered with a big brown sheet, but the orc is not being watched. The traveling showman has the keys always on his person, though the players may be able to simply pick the lock. The orc will also want to take revenge on the showman, but the players might be able to talk him out of this. If the players free the orc, he might be responsible for a horrible crime later on in the campaign, if the DM wants to include a bit of a moral dilemma.

The shake down
A couple of local guards are forcing a poor farmer and his wife to pay their taxes, and give up their last bit of money. The farmer pleeds to the guards that they need the money for food, but the guards show little understanding for the farmer's plight. The guards will not shy away from roughing up the farmer a bit in order for him to give up his carefully hidden coins. The players can intervene and try and convince the guards to leave the farmer alone. If the players do not intervene, the farmer may beg the players for help after the shake down.

Lifted Spirits
The players come upon a beautiful vista that lifts their spirits. The beautiful sight gives them renewed energy, and allows them to pick up the pace. Plus they get advantage on checks for the next 2 hours, and they can continue their journey with replenished stamina. Use this encounter along with a noteworthy location.

A proper burial
A woman begs the priest/druid/paladin of the party to give their husband or child a proper burial. The woman wants this person to be puried properly, and with the correct rites, so they may pass on into the afterlife safely. The PC deepens his/her faith with their deity by doing so, and gains the favor of their deity for the rest of the day. The DM may grant the player replenished spells, or advantage on certain checks for that day.

Bat Caves
The players have to navigate a tiny road along a cliffside that passes right several small caves. The caves are home to large swarms of bats that will swarm the players if they make too much noise. If the bats swarm the players, they must make a Dexterity (balance) save DC 15, or lose their balance and fall. The players can also choose to climb the cliff, but here they'll run into another encounter.

The Rock Sprite
The players encounter a sprite who disguises himself as a small rock. If the party includes a ranger or druid, they may be able to communicate with the sprite and ask for directions (or help). Otherwise the sprite will flee.

Infernio, the Dueling Wizards Spectacular
A group of traveling wizards put on a spectacular show where they stage a mock battle between three wizards. The show is a combination of cantrips and actual firespells, so the audience can feel the heat, and feels a sense of danger. Large wooden set pieces are rigged to collapse, to show a mock castle being blown apart. But part of the show goes awry when one of the wooden towers falls the wrong way, and hits a nearby house. The house immediately catches fire, and a beautiful woman emerges from a window, screaming for help. The players can kick into action before the guards do, to save the woman. As they lift her up, the front of the house falls apart, thus revealing the house as part of the set as well. The players receive a huge applause from both the audience and the wizards.

Smuggler's Tunnels
The players encounter a large wooden hatch, hidden underneath the sand, out in the wilderness. The hatch leads to a network of smugglers tunnels, which lead to a nearby hidden location/building. The tunnels may have enemies in them, in the form of smugglers or bandits. And the players may be able to find some elicit goods. The local authorities may give a good reward for handing in these goods, or the players can try to sell them themselves.

Starlight Canyon
This canyon is covered in ancient drawings that are only visible at night. The drawings light up, showing images and/or maps that may be relevant to the plot, or tie into local lore of the area. The DM may choose to make this canyon also home to special fairies that have some affinity to the stars or the moon. The glittery dust that covers this canyon is stardust, but only if it is collected in the canyon at night. It can be used as a special magical ingredient for crafting potions and/or magical weapons. Collecting the dust takes a while, because it is only the top layer of the canyon that is covered in it. So the DM can limit how much dust the party can collect at night merely by how many hours it takes to collect dust. Optionally the DM could even opt to have the magical aspects of the canyon only activate under a specific celestial alignment, there by making this encounter a one night occurance.

Shudder Storm
The region is struck by a haunted storm that lasts 1d4 days. The effects of the storm are a constant downpour, that obscures sight, along with ghostly visions that appear in the rain with every lightning flash. The party may see visions of deceased relatives or loved ones, and they will seem to call out to them, although the visions are obviously not real (no check required). The downpour is accompanied by an unnerving howling of the wind that sounds completely unnatural. The shudder storm may cause many local stores to close until it passes, and the party has disadvantage on everything while they are in the storm. While inside any building, the structure of the house constantly rattles, as if the storm is made out of a thousand angry hands trying to rip the house apart. The cause of the storm may be whatever villain or plot the DM has planned. For higher level parties, the DM may opt to also have actual ghosts emerge from the storm and attack players and villagers. The ghosts cannot enter houses, and can only attack outside.

The traveling rock elemental
The party encounters two children (a boy and a girl) riding on the back of a giant rock elemental. The rock elemental is a giant towering figure, slightly hunged, with the children riding on its moss-covered back. The children have tied all their belongings on the back of the elemental, and travel wherever it goes. Although the kids cannot communicate with the elemental, they consider the elemental their friend. If asked, the kids will share a story of how they lost their parents to a local threat (insert big bad here). They ran, and hid behind a rock, when the rock suddenly came alive and protected them from their pursuers. They have stayed with the elemental ever since, tying their belongings on its back, and traveling wherever it goes. The elemental doesn't move fast, and once per day it pauses for about an hour, before continueing on its way. The kids do not know what its purpose is, or where it is going. The party can travel with the kids and their elemental for a while (the DM may decide if there is more room on its back), until their paths diverge. The elemental will attack any enemies that they encounter along the way.

The Magic Tower
The party encounters an old tall tower, leaning over a river. The detailing in the masonry and woodwork is quite beautiful and whimsical, full of engravings of faces and of various strange creatures. The window shutters are open, and some clothes are drying in the wind. The rooftop is pointy and slighty bended, and there's a small hole in the roof. A bucket is lowered down to the river with a rope, and then pulled up again. But the players cannot see anyone from ground level. A small wooden balcony surrounds the exterior of the top floor of the tower. The door to the tower is locked, but if they knock, it will unlock itself. The tower is full of animated furniture (the furniture can be hostile or friendly, DM's choice). It seems the original owner of the tower is long gone. Animated brooms keep the tower clean, but the players will spot some cobwebs in spots where the animated furniture cannot reach, thus hinting at the age of the tower. The first part of the tower is just a stone spiral staircase, with three floors at the top. The first floor is a living area, the second floor an alchemy lab, and the third is a study, with a door to the balcony outside. The players will find some potions and spellbooks in the tower. The spellbooks may contain some new spells for the players to learn, and the DM can randomly decide what potions they find. The tower also provides the players with a view, allowing them to spot distant tall structures and landmarks.

The Haunted Swamp
The party encounters a misty swamp, where a strange singing lures them closer. Many of the plants and trees in the swamp are withering, and clouds of mosquitos hang above the water. Strange flickering lights can occasionally be seen in the mist, coming from the center of the swamp. The swamp is home to a small group of swamp witches. They dress in long immaculate white gowns (unstained by the swamp), and try to lure travelers into the swamp to eat them. They can emerge from below the water whenever a player heads to far into the swamp. They may also have tree ents to protect their swamp, if the DM wants to increase the difficulty of the encounter. Alternatively, maybe the players can convince the witches not to eat them, and the witches could provide them with help, or offer them a quest in exchange for help.

Stonehenge
The players encounter a man-made formation of stacked stones, similar to stonehenge. Depending on the season, druids might be seen performing rituals here at night. This location boosts the effects of healing spells, scrying and any rituals performed within the circle.

The hero on the hill
A proud stone knight stands on a hill, his sword reaching for the stars. At night perceptive players may notice an uncanny resemblance between the knight and an identical looking star sign, shining up among the heavens. Local legends say the knight was rewarded with eternal glory by being transformed into a star sign, forever watching over this world and shining his light on it. Monsters and villains stay clear of this hill, and the players can sleep here safely, under the protection of the star sign.

The overgrown mural
The party passes a rockface, overgrown with ivy. If one of the players succeeds on a succesful perception check DC 12, they will notice that the plants obscure a beautiful mural. The mural may have some relevance to the main plot of the campaign, or hint at an important historical event in the region.

The kings with no faces
The party passes a row of tall stone statues of ancient kings. The statues were carved from a nearby rockface, and their backs are still part of that rockface. The faces of the statues were destroyed long ago, and their names are now long forgotten. The party can climb up to the top of the cliff via a nearby stone staircase, and get a better look at the lay of the land. The DM can roll for a new encounter that the players see nearby, but it is up to the players whether they want to investigate or avoid it.

Dream Fruit
The players encounter a spring, where fairies circle around a strange tree, like tiny bright embers. The tree has a strange blueish color, and yellow spiked fruit grows from it, unlike any kind the players have ever seen. If the players consume the fruit, they fall into a deep slumber, where they experience a vivid collective dream. If some players do not eat the fruit, they still appear in the dream as themselves, but their characters will not remember the events from the dream afterwards, or experience the side effects of the dream. In the dream the players are taken on a dreamquest by the fairies, where they uncover important information regarding the main plot. Upon waking up a day will have passed, and those who fell asleep feel well rested, and are fully healed. If the fruit is taken away from the tree, it quickly spoils and no longer bestows its magical dream effect. While the players are in their deep slumber, they cannot be woken until a day later. The effect can also be dispelled as if it were a sleep spell.

The Beartrap
The players hear the desperate sounds of a wounded medium-sized animal stuck in a beartrap. The DM can roll randomly for the type of animal, or decide if it is a bear, wolf, panther, velociraptor, elk, unicorn, or anything that could make for a fun animal companion. The animal will need to be calmed with a succesful Handle Animal check DC 12, and opening the beartrap requires at least a strength of 10. If the PC that frees the animal has an affinity to animals, the animal may become an animal companion. It will either stay with the PC, or follow him/her on their travels. Otherwise, the animal flees back into the forest, but fey will hear of this kindness.

A Hairy Situation
The players come upon a house where locks of black hair have grown out of the doors and windows. If the players cut their way into the house, they will find a poor man pleading them for help. He was cursed for insulting a witch, and his hair has been growing endlessly ever since. Whenever he cuts his hair, it grows back even faster. His hair has spilled all over the house, and all the furniture. He is no longer welcome in the nearby village/city and people shun him because of his condition. He pleads the players to remove the curse, or otherwise convey his apologies to the witch on his behalf (he is unable to move in his current condition). As a reward the man will offer the players gold, or maybe even offer to join their party.

Random encounters will destroy a game faster and more seriously than pretty much anything else, it is best to rethink how you think about them.

They are not isolated random encounters. In an adventure the random encounters are part of the world, they might be paid troops doing guard routes, or some other party with their own mission. They should offer potential for information gathering or sub quests etc..

If you look at some of the more thought out "random encounters" people have posted, they are good because they each could expand into their own adventures or even campaigns if the pcs wanted to interact with them in a more complex way.

If you are truly out of ideas and just need the pcs to engage with something to keep them engaged, dont roll on a random encounter table. You want your PCs to meet something interesting and with a little depth after all. First roll on teh DMGs adventure / theme / goals / villians / introduction tables, so what they encounter is not a one dimensional XP extraction service. Then with this information you can setup the encounter and the situation the pcs encounter them in.

The next one is especially good for low-level players without much money. Can be tied into a quest without much effort.

Toll booth
When traveling towards a city, the party passes a toll booth, which is built in the middle of nowhere. The worker there charges a high amount of toll for access to the road, acting rudely and not showing any affiliation with any city or country. It should cause confusion whether this is fake or not. The players can each individually pay, and receive a token. The party can also continue without immediate consequences. No guards will block their passage. However upon arrival at the city, they must show their toll-booth-tokens to get access to the city. Guards will charge a lot more for access without token (it is a fine). There is a box full of tokens in the gaurd's office, so stealing tokens is an option to avoid the fine (although probably quite dangerous).

Lets have some more encounters to mess with the player's pockets.

Fortunate Rain
It starts raining coins from the sky for a few minutes. Each player can gather around 1d10x10 gp. As soon as the magical rain started, it ends again. Any coins not collected will vanish from the ground, while those that were collected stay in the player's pockets.

Graverobbers
Three men are busy digging up bodies and stealing golden teeth, rings and other valuables they can find. Two of the men are digging, while a third is carrying some old worn tools. If spotted by the players, they will give them an angry look. If approached, they'll try to drive the players off, without answering any questions about what they are doing there. The graverobbers want to avoid getting into an actual fight with anyone, or into any confrontation with the local guards. But they'll try to come across intimidating, to put an end to any inconvenient questions. The players can drive them off and then decide what to do with the open graves. If they rebury the dead, they gain the blessing of a deity for that day. If they rob from the dead, they can find around 1d4 valuables, worth between 1 and 10 gp. The DM may also bring up other roleplaying consequences for the players taking part in the graverobbing themselves.

The Silver Pool
A deep, calm pool has formed at the bend in a brook and when the light of the moon hits this pool it shines like liquid silver. Many of the residents of this village seem to have a large amount of silver in their households - tea services, plates, cups, cutlery, etc - and none of it appears to have tarnished. The locals are hesitant to talk about it if questioned - guarded, but not hostile. A typical response is "blessings from the Moon Goddess" (or whatever is appropriate for your setting). Further investigation may reveal that local legend says that any metallic item placed in the pool on the night of the full moon is turned to silver. Whatever metallic objects are placed in the pool at dusk on the night of the full moon are transformed into silver by sunrise. Keep in mind that the pool is deep, so casting items into its depth may not be easily retrieved. The locals use baskets with a rope tied to it. If any humanoid is within sight of the pool from moonrise to sunset, the magic does not work and the items placed in the pool are the same as when they were placed there. Metal weapons placed in the pool are considered 'silvered' as per page 148 of the PHB.

Hungry Wolves
A pack of hungry wolves closes in on the party over a period of several days. At first the party hears only howling at night. But soon they may spot the pack following them from a distance, but getting closer and closer. The wolves clearly look starved. After stalking the party for a few days, they eventually attack at night, by trying to drag one of the PC's away from the rest of the group. The players may chase them off before this attack happens. The wolves will flee if the players are putting up a fight. If the players leave food for the wolves, they will give up their pursuit as well.

Tar pits
The players encounter several bubbling pits of tar. The remains of ancient creatures can clearly be seen half submerged in the tar. Optionally the DM may have one of these skeletal ancient creatures come alive as a giant skeleton, if the players get too close. The skeletons may be of dinosaurs, or some other ancient beast.

The collapsed rope bridge
As the players cross several rocky crags, they come upon a large elevated plateau, raised from the earth. To reach the plateau they would have to cross a large pit 20ft. deep and 40ft. wide. The old rope bridge that would normally bridge this gap, has collapsed a long time ago. The old rope bridge now dangles from the side of the plateau, and is only still attached to that side of the gap. The players can climb down into the pit, and then use the rope bridge to climb up again, if they trust its integrity. Alternatively they can try to travel around the plateau, adding 2 hours to their travel time.

The forgotten battlefield
The players cross a large field where a massive battle must have taken place a long time ago. Several ancient catapults and ballistas lie in ruins, while the field itself is littered with skeletons and arrow heads. The players can search the battlefield for weapons and arrowheads, and may find some that are still in good condition.

Town on top of a creature
The party encounters a town that has been built on the back of a gigantic sleeping/dead creature. The DM can decide whether there's any risk of the creature waking up. But considering that an entire town was built on top of it, it would need to be something substantial to wake the creature up after all these years. The people in the town are confident that the creature will not wake up, or is definitely dead. The DM can pick a creature for these scenario, or roll a D12 randomly to have it be a:

1: Dragon
2: Giant
3: Golem
4: Tarrasque
5: Machine
6: Giant Turtle
7: Animated Object
8: Dinosaur
9: Leviathan
10: Monstrous Vermin
11: Sea Monster
12: Siege Crab

Ooze Pool
The party encounters a pool that looks like its made of water, but is in fact a giant ooze, waiting for curious adventurers to approach it. The pool may have signs that telegraph the danger, such as various objects left over after devouring its victims.

Mimic Town
The party encounters a ghost town, where all sorts of objects are mimics. The town was abandoned after a huge magical mishap, that transformed lots of furniture into mimics... sometimes even entire houses.

Rust Valley
The party encounters a valley full of rust monsters. Looking down on the creatures, they can see just how many of them are basking in the sun, and they seem completely unaware of the players. The creatures seem attracted to a vein of iron ore that lies exposed throughout the valley. At night the creatures rest, and the players can sneak past them unnoticed. They can also decide to go around the valley, which easily adds 2 days of travel time to their journey.

The Antagonistic Artifact
The party comes upon a tall stone artifact, inscribed with various mysterious runes. A loud and ominous humming emanates from inside the artifact, and the ground softly trembles as the sound oscilates. Surrounding the artifact are many dead creatures, and also several creatures that are still alive, and that are fighting each other. One of the creatures may even be a human npc. The creatures fight each other to the death, and stay near the artifact until they starve. If the players get too close (15 ft.), they must make a Willpower save or suffer the same effects, thus pitting them against their own friends. Anyone that succeeds on the save, is immune to the effects of the artifact for the rest of the day. The effects of the artifact can easily be dispelled, thus freeing the affected creatures from the mindcontrol, and allowing them to resume their normal behavior.

Low Gravity
A large crashed meteor buried underneath the soil, is leaking magic, and is causing low gravity in the surrounding area. Trees are much taller, there are sandstorms (because the sand is almost weightless now), a waterfall flows diagonally, and the jumping height and distance of any creature in the area (including the players) is doubled, as long as they are in the vicinity of the meteor. Towards the centre of the crash site, the gravity is even lower, with rocks tumbling in mid air, and bubbles of water drifting through the air. The jumping height and distance of creatures is tripled closer to the meteor.

A game of Knights and Dragons
The players encounter two old men playing a popular local boardgame called "knights and dragons" against a local farmer. The three are betting modest amount of coin on the game, and it seems just about anyone can join in and make a bet. The game itself is played with small wooden pawns in the shape of simple knights, dragons and castles. The rules are simple to understand, but there is a surprising amount of depth to the strategy in the game. The farmer seems to make a lot of obvious mistakes, while the two men seem to be roughly of the same modest skill level. The two old men will let the players win the first game on purpose (the farmer is a plant, working together with the two old men), when the amount of money is low. But they will suddenly play a lot better once the stakes are higher, and conspire to try and win a lot of money from the players. You can resolve the game with an int check for each participating player, where the two old men have an int of 16, but have disadvantage during the first game. Once the stakes are higher however, the two old men have advantage on their check.

The War Memorial
The players encounter an old knight at a war memorial. The knight, called Sir Valrick, is dressed in plate with a purple cape, a white beard and a balding head. He is kneeled next to the monument with his sword resting on the ground. His horse is tied to a tree nearby. The knight is remembering his fallen brothers during a pointless/important battle, of which he was one of the few survivors. Now the knight is often chastised by the locals for being a coward and not dying a heroes death. With a successful charisma (Persuasion) check DC 12 the knight will share his tale, and with a DC 16 he will even offer to join the party to reclaim his honor. The knight will also give directions to the party if asked, and knows all nearby settlements.

Where there's smoke
The party sees several plumes of black smoke in the distance. A group of monsters is raiding a nearby village, and is setting fire to the farms.

The cursed farmstead
The party arrives at a large abandoned farmstead. There are many swarms of flies, and the thick smell of rotting flesh hangs in the air. There are signs that attempts were made to set fire to the farm, as several parts of the roof have charred holes in them. Inside the farmstead the players find blood stains, but no bodies. Lots of crows sit perched on the roof and nearby trees as well. If the players investigate the stables, they are attacked by zombie cows.

Keep it safe!
While at a local settlement, a mysterious wizard runs into one of the PC's and presses an important item in their hands, before being arrested by the guards. What is it? What is it for? Why is it so important?

The young thief
While at a market, one of the PC's notices a young boy stealing some fruit. Do they alert the merchant, the guards, or allow the boy to get away with it?

Sorry, but I couldn't resist joining in! This thread is massive, so my apologies if someone else has made similar suggestions earlier in the thread!

If A Tree Falls in the Forest:

Looking for a spot to cross a crevasse deep in the forest, the party comes across a long-abandoned Elven fortress built into a massive hollowed-out tree, which has fallen over and now bridges the crevasse. The party can cross the by delving through the inside of the tree, exploring a ruin now resting on its' side. Enemies include giant ants which have weakened parts of the structure, spiders whose webs and burrows fill the stairwells, and ancient Elven ghosts who haunt the ruins, still existing in their original orientation (i.e. sideways on what are now the walls).


The Rooftop Chase:

After a night's drinking in a tavern, the party stumbles out just in time to witness a dozen small creatures climbing out of the upper-story window of a nearby building, carrying the struggling form of a small child bundled up in a net. The figures scurry off across the rooftops with their victim, leaping from roof to roof and occasionally hurtling roof-tiles or loose bricks at any pursuers- the party may chase them from street level or climb onto the rooftops to give chase.

The creatures could be Derro, Meenlocks or Goblins, and their intentions for their captive could vary (but are probably not good). They may be part of the schemes of the big bad, or it may a crime unrelated to the current plot (or a set-up for a future quest). Depending on how extensively the party enjoyed themselves in the tavern earlier, they may have disadvantages in hitting targets, climbing or simply keeping their balance.


The Ceremony:

The party learns that the answer to an ancient bit of lore they need (perhaps the means to attune a magic item, or the key to a villain's weakness) was once known by a tribe of Lizardfolk, who have incorporated it into an elaborate ritual performed by masked dancers and musicians in elaborate costumes. The party can try to spy on the ritual from a distance with some hopes of getting part of the information they need, or can steal costumes and infiltrate the tribe's ceremony. If they can pass the skill-tests required to keep up their ruse and perform the ritual, they will learn all they need.


The Giant Rampage:

The party stumbles across a small village being attacked by a Storm Giant. The Party can simply fight him, but those who dig deeper into his motives will learn that the giant's family is being held hostage by a band of Hill Giants led by a particularly crafty specimen, who are forcing the Storm Giant to raid for them. If they want to help, the party will need to either launch a very difficult assault against the hill giants, or sneak in and somehow smuggle several giants out from under the Hill Giants' noses.


Wild Night:

While taking a long rest after traveling, the party awakes and discovers that three days have passed and they have no memories of what happened. They awake at their campsite alongside an insane satyr named Bolumbo, they all have bizarre tattoos, there is a Displacer Beast curled up sleeping among them, one party member is holding a bloody knife, and a gang of evil cultists is searching the area for them. They'll need to retrace their steps from the last three days to unravel what happened.


Two-Part Harmony

The party meets the fleeing survivors of an orc attack, who report that the raiders were helped by a tribe of Ettins, one of whom had an amazing singing voice. A bit further along they meet a traveling showman who is following the tribe- he offers to hire the party to help convince the Ettin to leave her band and join his act. This may be complicated by the fact that she is the daughter of the chief, and that one of the heads is more inclined to join than the other.


The Pleasure-Barge of the Emerald Duke

As the party travels alongside a river, an ornate boat floats past in obvious distress: the oarsmen are missing or dead, cries for help can be heard from below decks, and some sort of massive aquatic creature can be seen trailing the boat. More ominously, the boat is heading towards some rapids the party passed a short time earlier.

More riffing:

Horse-sense
The party encounters a very pleasant inn and stable run by a large extended family, renowned for the extraordinary horses and ponies they rent for extremely reasonable rates. In fact, the entire family are Werehorses, who pose as ordinary horses to spy on riders (who never suspect their horses are listening in as they discuss their travel plans)

The family may be spying on behalf of a band of highwaymen, or the big bad in your campaign, or someone like the Harpers who are trying to do good behind the scenes. The party may notice when one of the horses is stolen that the family seems inordinately upset about having lost a horse, or their horses might take them off the path they intended.

The Festival of Gourds
The party wanders into a small town that is in the midst of their quaint harvest festival, which involves the gathering and carving of large gourds. If the party inadvertently interferes with the ritual, they discover the truth- the festival every year holds back a curse that prevents the gourds from coming to life and devouring every citizen of the town.

The Corpse-Flags
The party comes across a desolate hilltop lined with stout wooden posts. Flapping atop each post is the flayed and tanned skin of a person- some recent, others years old.

In fact, this is just the burial practice of a very obscure cult, and there's nothing particularly sinister about the posts or the people who erected them. Still, unless someone in the party passes an appropriate skill check, they're liable to treat the nearby village with apprehension that isn't really warranted.