How easy it is to design an adventure/dungeon...
Determine "level of adventure"
Determine XP pool for adventure (Solo monster x10)
Spend XP on quests, monsters, and skill-challenges
Determine Treasure Packets
Place on Map (if needed)
Arrange to Taste, allowing for a couple "off the cuff" ideas if the PCs do something unpredictable...
And yet ... I would say this is a way to generate a set of random encounters ... not so much an adventure/dungeon.
My adventures have always started with a cool idea, and with a whole lot of interacting
reasons for why there are monsters in a particular location, and why there is a problem.
A simple idea: A long time ago, a dam was built across a river. Over time, that silted over, creating a wide bog. Within the bog are the ruins of the dam, including a lock.
More recently, a necromancer made use of blocks from the dam to construct a tower. The tower is directly over the lock.
Very recently, the necromancer died. Monsters invading his tower are steadily converted into undead, and have been wandering downstream into a populated area.
Encounters: A couple of undead at a town that is downstream. A talk with the town elders. An encounter with spiders in the bog, maybe with other bog critters. A pit trap at the entrance to the tower, with a fall into the lock (along with a couple of undead trapped there). Another encounter with undead in the tower, including the undead remains of the necromancer.