THIS DUNGEON IS UNSTABLE!

This used to be the way out.

For use when the dungeon itself becomes structurally unsound.
Roll d6 once/turn, roll below on a 1-2.

d12
1. Menacing rumbles, distant sound of stone grinding upon stone, ominous cracking, crumbling from walls, floors, ceiling, adventurers get away with a warning this time
2. Subtle shifting causes doors to jam, must be smashed but doing so results in possibly injurious door jamb collapse
3. Loose flagstone underfoot, intermittent tremors create slip-and-fall situation for adventurers/ambulatory monsters, 1-in-6 chance of spectacular wipe-out when attempting anything strenuous; oozes, jellies, puddings, and slimes don't care
4. Sudden fissure opens up in middle of chamber, corridor, cavern (see Sudden Fissure sub-table)
5. Entire wall suddenly collapses, reveals adjacent dungeon area (or previously unknown dungeon area)
6. Noticeable trickle from ceiling, disturbing water flow on either side of corridors, stairs a nightmare of cascading waters, dungeon pools, cisterns, streams swell, rise above their embankments, water beasts seem pleased with increasing access, remember scores to settle with terrestrial denizens
7. Ceiling tiles, stalagmites, chunks of masonry drop at random, equal chance to smash friend or foe
8. Like a thing alive, column/statue/stalagmite/etc. suddenly topples like its aiming for adventurers, will defy laws of physics to come down upon chosen target
9. Intense tremor causes room'/chamber/corridor to roll, pitch, & yaw wildly for 1 minute, comes to rest in awkward position, may cut off access to adjacent dungeon areas
10. Major seismic disturbance: PCs, monsters, set decorations tossed around for ten minutes, again, the oozes don't really mind
11. As per entry 10, but non-stop shaky-cam sequence until dungeon evacuation
12. Sudden catastrophic super-tremor for full turn: free-fall alternates with injurious slamming against floor and ceiling 2d4 times, even the oozes seem to hate this one

Sudden Fissure sub-table
d6
1. pit: 3d6 feet wide, 1d12x10 feet deep
2. pit, semi-bottomless, eventually fall up out of a well in dungeon in adjacent dimension
3. opens into chamber full of one million terrified bats
4. as per entry 1 plus copious poof of toxic gas
5. as per entry 4 plus surrounding floor cracks 20 feet in all directions, will collapse in 10 seconds
6. Satan (or local equivalent) rears up from below, wreathed in flame, howling with laughter