An endless stream of random encounters

The Necromancer
The party encounters a small rural village, where the locals beseech them for help. They explain that a foul necromancer and his band of evil dwarves have been working to resurrect their dread deity in the hills a few miles away, and are responsible for the disappearances of several innocents. The townsfolk have staged a few guerilla raids against the necromancer and his forces, but lacked the strength to mount a real assault against their foe- until the party's arrival, that is.

In truth, the "Necromancer" is a wealthy scholar from a far-off land who has found through Divination the bones of a massive, monstrous creature from legend. He has hired a tribe of dwarves to help excavation the massive skeleton- the dwarves, who were facing hard times after exhausting their mine, are glad for the paying work.

The disappearances of villagers is completely unrelated to the scholar and his dwarven hirelings- if appropriate to your main plot, the missing villagers may have fallen victim to the Big Bad of your campaign, so what seems like a side-quest may actually be a part of the main plot after all.

As an added wrinkle, even though the scholar's intentions are sincere, that doesn't mean his excavations might not awaken something terrible after all.

The Hunt
Crossing through the wilderness, the party falls prey to the trap of a Rakshasha and his Lamia consorts. He explains that he is hosting a banquet of other powerful evil beings, and for the evening's sport they intend to hunt the party. He will outline a set of preliminary rules for the contest- basically, whoever can reach the edge of his estate is free to go. If the Rakshasha is vastly more powerful than the party, good uses of skill checks may convince him to accept some handicaps to make the contest more sporting. There may be some other people being hunted at the same time- some may be potential allies, some may be out to betray the party to save their own hides, and some may be hapless innocents that put the party in a difficult situation.

The Dryad's Toll
The fastest route toward the party's destination takes them through some enchanted woods. There is a path running through the woods which is smooth and safe, with resting spots along the way- it is as comfortable as overland travel gets. The Dryad who oversees the forest, however, demands a toll be paid by all who use the path- not in coin, but in blood for her growing garden of carnivorous plants. Where the blood comes from is not something she worries about too much. Her small army of pixies guarantee that those who refuse to pay the toll and still use the path are harassed every step of the way, while her faithful band of centaurs ensure that leaving the path is not an option.

The Anthills
The party finds a series of interesting ant mounds among some rocky plains. While of ordinary size, these ants appear more intelligent than most, with tiny cart tracks snaking between the mounds and minuscule chimneys suggesting hearth fires or even forges beneath the earth. The ants appear to be industriously separating gold flecks from the sand, and it appears they've built their colonies above a vein of gold.

If the party aids the ants in some way (leaving them food, for example), the ants will reward them with enough grains of gold to be the equivalent of a gold coin. If the party can find a way to telepathically ask the ants a question, they will spell out one-word answers with their bodies to any question they might reasonably know the answer to.

Should anyone harm one of the anthills, they will instantly be magically shrunk down to the size of a grain of rice, and will have to contend with the now very angry (and proportionally pony-sized) ants.

The Witching Pit

In the middle of the forest, the ground slopes down into a large pit. In the center of the pit is a large empty cauldron. At night a coven of witches, dressed in white garments, conduct rituals here. But the pit is abandoned during the day. The witches are neutral and worship nature. If they are disturbed during their nightly ritual, they could turn hostile. The pit is an excellent place for the players to perform their own nature-based rituals. An unearthly calm lingers over this part of the forest and animals here are very tame.

Impalement Hill

A large hill is covered in long wooden spikes, on which several people are impaled. The victims were probably alive when they were impaled. The players can search the bodies for valuables, though most valuables have probably already been taken.

The Sacrificial Stone

The party encounters a large flat stone, covered in blood and lined with strange arcane symbols. It is clear that the stone has been used frequently for some kind of ritual sacrifice. The DM can decide whether the blood on the stone is fresh, or very old. The stone itself is supported by several smaller stones, creating a sort of rough table. Optionally the location may radiate evil, if it has been used for evil rituals. If a priest consecrates the area, the stone breaks in two.

Wooden Effigies

The party encounters a dense forest that is protected by countless wooden effigies. The effigies are small-sized wooden carvings of men with spears, but at night they come alive to protect the forest. The effigies do not pursue invaders beyond the edge of the forest and are vulnerable to fire.

The Cursed Forest

The party encounters a strange forest where the trees are twisted into bizarre shapes. Strange glowing embers in various colors float through the air and the forest is covered in many odd looking mushrooms. The forest smells strange and the players also feel strange when they enter. Magic is in the air... but it feels wrong. Most disturbing of all, is that among the trees are many shapes of adventurers who have been turned into trees themselves. The players may be able to restore some of these victims to their original form, if they posses the right spells to do so. The forest is protected by dangerous Dryads, who curse any trespassers into wooden mockeries of their former self.

The Giant Ferryman

On the bank of a treacherous river stands a tall hollow tree with a mouthpiece attached to it, almost like a giant horn. The river is very deep, and swimming across seems like suicide. But if the players blow on the mouthpiece, a giant emerges from the other side of the river. This helpful Ferryman will gladly carry the players across on his shoulders.

Night Sprites

When the players travel through a forest at night, hundreds of tiny yellow lights appear on the trees and among the many plants and mushrooms. The lights are in fact friendly sprites, who are curious and helpful. The sprites only show up at night and cast enough light to show the players the way through the forest.

The Abandoned Gatehouse

The players arrive at a toll bridge, with an old gatehouse on either side. The bridge is an old drawbridge that is currently raised. The gatehouse seems abandoned, though there are clear signs that it was very recently in use. Chairs lie toppled on the floor and food on a table is barely a few days old. On the outside there are many holes in the square building and its roof, thus letting in a cold draft and plenty of rain. An eerie feeling takes hold of the players when they enter. A tiny spiral staircase leads up to the top of the gatehouse, from which the players have a good view of the surrounding area. Once again, there is no sign of any guards here. Lowering the drawbridge requires a strength check by operating a mechanism on the first floor, but a simple Knock spell will also do the trick. The reason for the missing guards is entirely up to the DM, but it could tie into the current plot, or there may be monsters that have taken hold of the structure (it makes for a great fortification).

Couldn't resist some more:

The City of Ash
While traveling through a mountainous area, the party stumbles across the partially-exposed city buried long ago in ash from a nearby volcano, which smoulders to this day. Lying strewn around the ruins are the contorted figures of the towns' doomed inhabitants, their bodies long ago encased in ash and gradually petrified. Their forms bear witness to their dramatic final moments- some posed in moments of bravery, of cowardice, of piety or of despair. The stone dead may arise under certain conditions, or perhaps it's just a way to unnerve the players on their way to the next adventure

The un-sunken city
A recent earthquake has pushed a chunk of sea floor up to the surface, partially exposing a once-underwater city of merpeople. There are trapped merfolk in need of rescue, water elementals once harnessed to serve the citizens that now run amuck, and marauding sahaugin taking advantage of the merfolks' plight to loot and enslave. Worst of all, a series of coral standing stones that once held an aboleth imprisoned have toppled, and must be located throughout the ruined city and righted before the next full moon.

Sepulcher of Horrors (with apologies to Jack Vance)
The party stumbles across a decadent tribe of Duergar (or possibly Derro) that bear artifacts from a centuries-old lost civilization, but which appear almost as new. If the party investigates, they discover to their horror that the evil dwarves tunneled into the hidden chamber where the ancient civilization hid themselves away in timeless magical slumber, intending to reawaken when some calamity had passed. Instead, the dwarves have been excavating the crystalline pods the people slumber inside, smashing them open and using the unfortunate inhabitants for food, slave labor or hideous tortures.

The Inverted Castle
An earth-mote has long floated over the countryside, topped with an ancient wizards tower long known to be magically sealed. In the aftermath of a massive storm, it is discovered that the mote has flipped over entirely, and the top of the now-inverted tower barely grazes the treetops as it drifts along. What's more, part of the roof has been shorn off, allowing access to the interior of the tower for the first time in living memory.

Inn of the Wayfarer
Deep in the desolate wilderness, after days of grueling travel, the party is surprised to find a warm, inviting inn standing where their maps show no such structure. The Inn is a pleasant place, albeit crowded with an assortment of odd patrons unusual for the surrounding area.

In truth, the Inn travels every few days between the planes, on a random journey through the multiverse. Anyone who stumbles across it can enter, stay for as long as their funds allow, and then step out a few days later into an entirely different world.

Sometimes the Inn shifts to a dangerous plane, such as a layer of the Abyss or the Shadowfell. In such times, the patrons are often drafted to serve as the Inn's defenders as horrible creatures lay siege to its' walls.

The Frozen Fleet
Deep in the ice fields of the far North, the party stumbles across a small fleet of ships, frozen decades ago in the ice. The survivors have built a colony of sorts, connecting the shipwrecks with rope bridges and huddling around fires they zealously tend. They send out expeditions to scavenge a pine forest some ways distant for firewood , and survive on fish and seals caught through holes in the ice. Unfortunately, cannibalism has become a way of life among the survivors, and they draw lots periodically to see who must fall to the chef's knives to sustain the others. When the rare traveler is encountered, they wind up in the pot instead.

The Colossus

The party encounters a gigantic stone structure in the shape of a warrior. It is large enough that the players hardly reach beyond its feet. The Colossus may be standing in a body of water (like in the middle of an important strait, or a river), it may be supporting an important structure (such as a bridge) and it may or may not have toppled. Optionally, the colossus may have arrow slits in its chest and head, so that it also serves as a defensive structure.

Fire whirls

The party encounters a desolate wasteland where small tornadoes of fire are formed from ignited gas in the ground. The Fire Whirls travel at a speed of 10ft per round and deal 4d6 damage on touch. If the DM rules that the cause of the Fire Whirls is magical, they may be dispelled, but they may also home in on the players on purpose.

Crannogs

The party encounters a small settlement on wooden poles in the water. The various houses are interconnected with wooden bridges, creating a sort of artificial island on stilts. The houses are made from timber, with pointy roofs constructed from straw and reed. Outside there are many fishing nets, as fish would be the primary source of food for a settlement of this kind. In case of danger, the inhabitants are probably armed with the same sort of spears they would normally use for fishing, though this is entirely up to the DM.

I realized I've been getting off track and writing whole adventure seeds rather than simple encounters, which I think this thread was intended for. Still, I came up with a couple more during my morning commute, so here they are. From here on, I'll try to get back on the encounter track....

The Lottery
The party comes upon a small settlement deep in the wilderness just in time to witness a grim ceremony. The youths of the village are solemnly placing their names in a bag, while the town elders look on sadly. At the arrival of the adventurers, the townsfolk perk up. They are drawing lots to determine whose 3 sons or daughters will be offered up this year to appease the terrible dragon that lives in the caves nearby. But surely these brave heroes can slay the beast and end this scourge, right?

The hitch is, there is no dragon. It's all a scheme put together by the mayor and a couple of the town's elders, who have staged the site of several dragon attacks over the years. The youths that have been given over to appease the dragon are actually meeting some other terrible fate in the caves.

If the party considers fighting the dragon, the mayor will at first try to discourage them ("if you fail, it is these townsfolk who will pay the price"), but if they insist he will offer the services of his best lieutenants- who will betray the party as soon as they enter the "dragon"'s cave.

The Test
The party emerges into a clearing and is startled by a terrible sight- two peasants cower in the field, as an immense monster (choose something well beyond the party's normal abilities) looms over them.

This is an illusion, cast by an elderly but powerful good-aligned archmage who might potentially want to aid the party in their current quest. He's using the illusion to judge the party's bravery and sense of justice: if they leap into action immediately despite the obvious risk, the archmage will be impressed by their heroism. If they hesitate, the illusory peasants and monster will all turn to the party and shower them with a series of elaborate insults before disappearing, and the archmage will look elsewhere for heroes.

The Dubious Airship
Along the road in some remote location, the party is startled to find a bizarre airship hovering above them, with a friendly-seeming fellow hailing them from overhead. The pilot and creator of the craft cheerfully asks for directions to his destination, which may or may not be along the party's path. If the party helps him, he may reappear later in the adventure at a fortuitous time, or he may offer them a ride aboard his creation. It is also possible that the ship is not as airworthy as it seems, and could lead to a side-adventure when goes wildly off course and crashes.

The Parade
After completing a particularly heroic adventure, the grateful townsfolk decide to host a parade in the party's honor. Riding horses at the end of a long procession of dancers, musician and actors performing skits demonstrating the party's heroics against illusionary foes, the party is showered with garlands and praise from the grateful people. Naturally, that's when the big bad strikes.

Watch me pull a Boggle out of my Hat
Looting a sack belonging to a defeated foe, the party is shocked when a long, wiry hand reaches out of the bag, steals something of value from the player, and disappears back into the bag. it turns out the bag is a variation on a Bag of Holding, but in this case the bag opens into a manor-sized pocket dimension staffed by a very temperamental boggle. The normal protocol is to ask politely for what you'd like before opening the bag, then offer the Boggle some food or money when opening the sack. Since the player presumably failed to follow instructions, the Boggle is now angry. The player(s) will need to go into the bag and either defeat the Boggle or make amends.

If the party is traveling through an area with volcanic activity, they may run into any of the following encounters:

Lava Flow

The party encounters a river of lava. If a player tries to swim in the lava, they take 10d10 fire damage, or 18d10 fire damage if they are fully submerged. The only way across is to either jump (if the river is not too wide), go around (which may add several hours to the party's travel time), or try and create a bridge. A tree could be cut down to form a temporary bridge, but it would then of course catch fire, and wouldn't last very long. A flammable object immediately starts to dissolve and sink into the lava, and thus walking across the object requires a successful DC 12 Dexterity (acrobatics) check to not lose your footing. Although the lava is very hot, the players can stand pretty close to it without actually taking any damage. The lava sheds bright light in a 30ft. radius, and dim light in an additional 30 ft. radius.

Pyroclastic Surge

A thick cloud of turbulent and pressurized gas erupts from cracks in the ground. These eruptions can be seen from a fair distance by the party. The clouds block all normal sight for creatures inside the clouds, and deal 2d10 bludgeoning damage per round, as the players are struck by rock fragments. Optionally a legendary creature could also strike the ground to create these cracks as a legendary action, and release such a surge from the earth.

Lava Fall

A lava fall offers the party an additional way to bypass a flow of lava, by passing behind the deadly flow as it drops to a lower level. Doing so however it not without its own risks. The lava splashes and sparks violently. Passing behind a lava flow requires a successful DC 10 Dexterity (acrobatics) check, or the player takes 1d10 fire damage from falling lava and may also catch fire.

Flame Spout

A flame spout is a dangerous fountain of flame and lava, usually from a lava lake or river. Flame spouts shoot upward from the lava, reaching heights between 15ft and 30ft., with a width between 5ft. and 15ft. Anyone struck by the flame spout takes 2d10 fire damage and may catch fire. Flame spout eruptions often last about 2d6 rounds, or they may even be permanent to an area. Flame spouts can give birth to Fire Elementals, who heal 1d10 hitpoints per round while inside the spout.

Pyroclastic Fall

The area in the immediately vicinity of a volcano is often struck by ash and falling rock from volcanic explosions. Depending on the wind direction, this debris can strike an area up to 8,200,000ft (1553 miles) away from the volcano itself and is propelled up to an altitude of 42,000ft. (7 miles). Any players in the area take 1d6 bludgeoning damage per round from falling debris. Some legendary creatures could also create this effect as a lair action, which lasts for 1d10 rounds, and covers the entire area that the creature is in.

Steam Devils

Any area where volcanic eruptions emerge from the ground, can give rise to a special kind of air elemental called a Steam Devil. A Steam Devil behaves just like an air elemental, only it deals boil damage whenever anything touches it, and it hovers just above the ground (it cannot fly). Any creature that is within 5ft. of the Steam Devil and touches it, strikes it with a melee attack, or ends their turn on the creature's space, take 1d6+1 boil damage. They then take the same damage at the start of subsequent rounds, for 2 rounds.

If the Steam Devil is of a size category larger than medium, add an extra die of damage (per size category) for it's boil effect. Boil damage only affects organic creatures (living or dead) and does not affect non-organic creatures, such as constructs. Boil damage does not stack. If a player takes boil damage from multiple sources, only the strongest effect counts. Boil damage counts as fire damage, for the purpose of resistances. A Steam Devil cannot set a creature on fire with its attacks. Steam Devils often appear in small groups of 3 or 4.

Lava lake

A lava lake usually forms inside a crater, on top of a volcanic vent. Volcanic lake's often have sudden eruptions of flame spouts (see above) and are often home to Fire Elementals. Sometimes semi-solid slabs of rock float on top of the lava, formed by debris broken from the side of the crater. Jumping across such floating platforms requires a Strength (Athletics) check DC 12, or the player falls into the lava, taking 10d10 fire damage, or 18d10 fire damage if fully submerged. Additionally, Lava Lake's often emit noxious fumes, similar in effect to a stationary Stinking Cloud (see the spell description).

Acidic Crater Lake

An acidic crater lake, is a volcanic crater that has filled with acidic water. The acidity of the lake can vary between mild (1 acid damage to organic creatures per round, no effect on objects), medium (2d4 acid damage per round), to strong (2d8 acid damage per round), which can dissolve a boat in mere minutes.

Boiling Crater Lake

A boiling crater lake, is a volcanic crater filled with water, with underwater volcanic activity. The heat from below causes the water on the surface to boil, dealing 1d6+1 boil damage to organic creatures (living or dead) per round, but leaving objects unharmed.

Rare ores

Due to recent volcanic activity, chunks of stone containing a rare ore have been ejected from a volcano and are scattered around the area. The players can harvest these ores and use them to forge special equipment.

The Wrong Place at the Wrong Time
While browsing the goods for sale in a busy market square, the adventurers end up next to someone in fine attire - possibly a successful merchant or local noble. He or she may have a retinue with them, but not a large one - a servant and possibly a bodyguard. The well dressed person suddenly grabs the back of his or her neck and falls to the ground. A successful Perception DC 20 catches a glimpse of a shadowy figure moving away quickly - possibly from a rooftop or dark alley. A successful Medicine DC 10 on the fallen noble finds a poison dart or blowgun dart in his or her neck. Maybe some bystanders also get hit by poison darts, maybe a party member - though a 'close call' of a poison dart hitting armor might be enough. Maybe the bodyguard blames the party member who was standing closest to the noble.

Mind your Drinks!
In a crowded tavern, a patron who perhaps should have headed home a tankard or two ago is bringing a fresh pitcher to the table for him and his mates. He stumbles and spills some ale on a large burly fellow who does not take too kindly it. He shoves the first man - if he does not out right fall over, the pitcher of ale certainly gets dumped and/or sprayed all over. His mates are upset at the loss of their drink and the rough handling of one of their own. The burly fellow has some irritable mates of his own. Other patrons either stand up, grinning or take to hiding under the tables. Unless someone does something to intervene, a brawl is imminent...

The Street Magician
An illusionist is performing on a street corner. The audience gathered to watch is mostly children, who cheer and clap enthusiastically, but do not have anything to toss into the donation hat - a battered well worn thing at the magician's feet that has mostly coppers and a few silver pieces in it. The illusionist's robes are quite threadbare too, but appear to be of fine quality.

I liked @Imaculata's volcanic environment ones so much, I thought I'd try my hand at some terrain based ones. Here are some arid and rocky environment ones

Dry stream bed
Travelling through an arid environment, this dry stream bed is easily the best way to make good time. It is hard packed sand with a few small boulders and small ponds that are easily avoided. The banks of the river and the surrounding area are rocky, rough terrain - perhaps the dry river is at the base of a gully leading into the foothills. For every hour travelling, roll a d8 - on a 1 it starts to rain (or determine the weather however you normally would). The rain is not a big deal at first - a stream starts to form, the adventurers get wet - DC 10 Athletics to stay on your feet. If they continue to travel on the river bed, bad things are about to happen as the rain flows down the rocky landscape out of the foothills. The stream becomes a river again before long - DC 20 Athletics to stay on your feet, or DC 15 to swim upstream. 1d6 bludgeoning on a fail and the character moves 10 feet downstream every turn (repeating swim check). Not long after that, the river becomes a torrent, bringing rocks and mud with it. DC 25 Athletics to stand, DC 20 to swim, 1d8 bludgeoning damage on a fail and washed 15 feet downstream every turn.

Dust Bowl
This ancient arid crater has filled with a deep layer of dust, sand and silt. Its tricky travel, but a group of hardy adventurers such as yourselves is not too inconvenienced by it. As you approach the center of the crater, the dust kicked up by your footsteps clings to the air more than you would expect. You all instinctively cover your mouths to prevent breathing the chocking dust. The dust starts to gain form in the air... solidifying and congealing into flying creatures around you.

The party finds themselves surrounded by dust mephits - an appropriate number to make the party think, but difficult to overcome. A successful Arcana DC 15 lets a character know that dust mephits are drawn to catacombs and find death fascinating - Detect Magic may reveal the mephits before they materialize too.

The Convenient Oasis
Its feels like it has been days since you've seen any plant life. It hasn't, but that's what it feels like. You have passed scrubby, twisted shrubs and tough looking plants, but nothing even remotely edible. You are not sure how anything survives in this blasted rocky terrain, but it does. You've managed to stretch your rations with the odd lucky catch of a rabbits, lizards and some kind of small goat-like creature. The water-skins you carried with you are getting perilously low.

As you climb to the top of a low rise, you can't believe your eyes! Green! More than that - a spring! Water! Fruit trees! As you make your way down the hill to the oasis, something starts to nag at the back of your mind. It seems oddly convenient that you discovered an oasis right when you needed it. Not so much discovered it as it was placed here - for you. Why? And by who?

The Falling Star

At night, if a PC is keeping watch, they are witness to a bright falling star. It shines an extraordinary bright light, and its descend is unusually slow. The star may bestow a blessing on the party (advantage on checks the entire next day), or grant a wish as per the spell of the same name. The crash site is now a blessed area, full of roaming fairies and blossoming flowers. They can collect star dust here, which is a valuable magical component.

The Dark Star

At night, if a PC is keeping watch, they see an ominous red star with a pitch black core, crash to the surface. The falling star leaves a long orange trail in its wake, and crashes into the earth with a deep rumble and a bright flash of orange light. The resulting crater is littered with meteorite ore, which is a valuable crafting component for weapons and armor. However, the surrounding area is also infested with other worldly creature(s) (demons for example) that hitched a ride on the falling object. Surrounding plants and trees will be set on fire by the explosion, although probably not enough to instigate a raging forest fire.

Meteor Shower

At night the party can be witness to a meteor shower. Bright orange streaks of light shoot across the sky every few seconds. Clergy can interpret this as an important sign. It could be a sign of good fortune, or a warning of things to come (depending on how the DM fits this into the plot).

Guiding Star

A bright star appears among the heavens, guiding the party to their destination for the next couple of days. The star may be the blessing of a deity that wishes for the party to succeed, and clergy may be able to identify it as such.

The Star Sign

A rare sight appears among the heavens; a star sign that is usually not visible, because the stars are too dim. Tonight though, its stars shine bright, and inspire clergy and bards alike. Clergy are aided in any prayers that they make at night, and bards can remember a song or tale about the star sign that they had long forgotten.

Roll a D8 to randomly determine the shape of the star sign:

1 - A knight. According to legend, this ancient hero completed a heroic quest that earned him a place among the stars. But his legend is now almost forgotten.
2 - A dragon. Legend has it that this great beast once sought to swallow the light of the stars themselves, before it was banished to the sky. One of its stars is red; supposedly its eye.
3 - A chariot. Legend has it that an ancient king once road a magic chariot into battle that could fly. But when he flew too high, he could no longer find his way back.
4 - A celestial. According to legend, during times of despair this celestial can be summoned to descend from the heavens and help to those who are worthy.
5 - A ship. This star sign has the shape of a strange airship. Legends tell of an ancient people who traveled beyond the stars and never returned.
6 - A turtle. The great turtle answers the prayers of those who are blessed to see its radiant light only once a year.
7 - A golden serpent. Its stars shine slightly yellow. Legend has it that this blessed creature once turned itself into stars to end a never ending darkness.
8 - An ancient god. This ancient deity was long forgotten. Its stars dimming further every year as belief in it wanes. Only once every few years its light flare up and the sign is revealed. The players can risk praying to this deity, but do not know its alignment.

Slow! Construction ahead
The road here follows the contour of the hillside, carved out of the hillside really, with a river running along the valley floor perhaps 50 feet below. Trade and travel upstream usually follows the road, while travelers dowstream typically use the river. However recent flash flooding and landslides have washed out sections of the road and the bridge that used to be about a mile up river. Finding a route around will take at least 7 days. The local lord's engineer and survey corps have made camp and have begun road reconstruction. Most of the laborers are locals that have been pressed (not totally unwillingly) into service. A smaller team of engineers and surveyors have made camp at the bridge construction site, but they are not soldiers. They are being harassed by creatures pushed down out of the hills, also affected by the recent landslides. If only the engineers had some protection while waiting for the lord's soldiers to arrive in 3 days time, they could probably finish the temporary crossing in 4 days

Shoeless
The party comes across a young centaur hobbling through the woods on three legs. The forth is being favored and it is unable to take the centaur's full weight without considerable pain. It is managing alright, but is still far from home and getting through thick brush or over fallen logs is proving to be quite difficult for the creature. It threw a shoe and ended up getting a sharp rock stuck in its hoof. It gladly accepts any assistance offered. If the party accompany it back to camp, the centaur looks for any excuse to delay or distract the party. His/her mare told him/her to visit the blacksmith and get re-shoed before heading into the forest and he/she is not looking forward to the chastising lecture that is surely coming.