Void adventure

This is a half-baked idea for a zero-prep procedurally generated adventure, but I think it might have some legs to it.

First, the characters successfully navigate a suspiciously short dungeon belonging to a wizard, eventually finding themselves in his library. The treasure is inches away. Then the door and windows slam shut, there's a light show and a dizzying sense of transition. If the characters pry open the doors or window covers, they find themselves looking out into true nothingness - the void. The room was a trap, and it caught them. They've been dumped out of the world entirely.

Presumably the wizard will eventually call the room back, if only to reset the trap. But there's a dead and mummified adventurer here, which suggests that it could be a good long time. They need to rescue themselves, not wait.

The dead adventurer had an escape plan, which he laid out in a journal he had with him. The room could be shifted back into the world by tracing the path of a specific rune on foot and chanting a magical phrase to undo the trap magic. The biggest problem was that a single room isn't large enough to trace the rune.  It needs to be many squares long. However, it was possible to call additional rooms into the void, from structures similar to this room in concept (IE. dungeons). Then the issue would be digging through walls for access, defeating whatever threats came across with the architecture and building a walkable path through them.

The final journal entry states that a terrible void storm had begun and he was returning to the library for the little protection the bookshelves offered. Whatever rooms he managed to add are gone. If the PCs want to follow his plan, they'll need to start from scratch.

Obviously the characters have specific wants in the rooms they summon: food, building tools and supplies, construction that allows them to create openings where they need them. They'd also prefer those rooms to be unoccupied. Each additional criterion adds 1d3 to the difficulty of the magic roll for the summoning. If I was running I'd keep the players in the dark over whether they pass or fail until the room arrives, and remove one of the criteria for every point they fail by. They get a room regardless, but maybe not the one they hoped for.

I like the idea of using the random dungeon generator from Donjon. Hit random each time to get a different dungeon style, but set Details to basic to get a list of monsters and traps. Roll a die to pick which room they get. If the encounter die hits while they're in that room, it's something from the wandering monsters list, arriving some time after the room they occupied.

The characters have to work fast, because another possibility on the encounter die is a void storm. Storms last 1d6 turns, and while they're in progress, areas of the map simply pop out of existence. Erased by the void. Generating those randomly seem like too much effort, so I'd get the players to map out the dungeon they're constructing and drop d4s on their map to determine where the lacunae occur and how many squares in diameter they are. (D4s are indisputably the most evil of dice. Bastard pointy things.)