There's a contest in an AD&D group on Facebook, everybody is to write a 21-word description of a dungeon room. It's a pretty fun challenge, so I entered two into the contest (#1-2) and wrote eight more. Could make good minor "Specials" for random dungeon stocking on the fly as well, I guess?
1. Library of Dark Wisdom
Gloomy hall, ceiling 40', labyrinth of 30' tall shelves, extra exits on top. Loud sounds trigger Silence spell. Undead librarians wander.
2. Shrine of the False Serpent God
Columns carved with intertwined snakes. Gigantic statue of god, hollow on the inside (priests fake miracles). Sacrificial dagger on blood-caked altar.
3. Trick Crypt
Eight stone sarcophagi (filled with harmless black sludge), arranged in star-shape. North-east one has false bottom, leads to secret underground passage.
4. Machine Room Orphan
Narrow space, cogs & gears, bursts of hissing steam. Lost child cowers in corner, amulet of the Witch King around neck.
5. Underground Cathedral of the Monster Hunter
Backlit stained-glass windows in alcoves depict famed monsters; if broken, glass shards animate, but can be used to create monster-slaying weapons.
6. Rainbow Room
Seven doors, each painted one color of the rainbow. Illumination cycles through spectrum, only the door with the current color openable.
7. Impractical Garage
Ornate chariot; entrances to narrow for it to pass. Pair of invisible horses neigh. Gilded weapons & tools hung on walls.
8. Draconic Gauntlet
Like a dog agility course, but for young dragons (tunnel, seesaw, hurdles…). Training manuals on shelves. Torn dragon harness on ground.
9. Creepy Anatomical Theatre
Horseshoe-shaped auditorium. Semi-dissected body on slab looks just like player character, but with animal features. Mad teaching assistant armed with scalpels.
10. False Chasm
Rickety rope bridge over chasm. Actual depth only 30’ – masked by illusion of void, tunnel to treasure vault at the bottom.