The community responded and below you will find ideas in unedited form. If I missed anyone I do apologize. The fun thing about this little experiment is the sheer variety that came from it. Keep in mind that on Twitter you are limited to 140 characters. So if you would like to add more material or use our little sunken ziggurat by all means please do. Just remember danger is everywhere so you may want to bring a few torch bearers and a 10’ pole!
@FailedGM: The cistern holds a hungry narwhal.
@Dungeon_Junk: You find a well-decorated room full of shelves containing valuable scrolls. They are all ruined due to the damp.
@Dungeon_Junk: In the armoury you discovered the legendary scimitar Godsbane. It's turned almost completely to rust.
@theAdjunctDM as the party enters the sanctuary, their torchlight reveals a portion of a massive, golden statue of a Yuan-Ti.
@theAngryGm The Sunken Antechamber: Swamp water fills this chamber to the knee. Most don't see the stairs under the water... Until they fall.
@seanbonney: Low ceiling honeycombed with overhead shafts. Most filled with trip-wire released bones and armor. A few with skeleton warriors.
@fiddleback: The Room of Hours. Upon entering this large sand filled room (difficult terrain), PCs are under the influence of a slow spell.
@jencilmonkey Huge clockwork gears grind inexorably, partially submerged in the sand, skeletons impaled on the cogs' sharpened teeth
@dmdandanfieldng The floor in the hall is under 6cm of water mixed with oil from a ruptured flame trap. Any spark will ignite the oil
@karakdamnaz You find a fountain spraying a rainbow hued liquid. Non-lawful PCs that drink heal 3d8+5 hit points.
@karakdamnaz A sloping room with deep water at the far end blocking exit. Dessicated frogs litter the floor. The water is an illusion, DC 28.
@medicmsh The vines coil & twine towards the light far overhead. Their carnivorous rootlets, however, coil & twine towards the nearest PC...
@bengrunzel The submerged gear room can drain water in one level, but a hydra-troll is stuck in the gears.
@spaceseeker19 Room with doors on 6 sides rotates forward each time it's entered, changing its location & dropping PCs to far wall.
@haelyn78 u find an altar of an ancient deity. Sacrifice an uncommon magic item gives u adv in the next 5 checks to locate traps/doors
@Aetherium83 Hall of Ancestors. A long passage w/ countless lines and symbols etched in blood identifying the lineages of the tribes.
@ThemDave carapaced bugs scuttle down a southern hallway using ceilings as floor. Perhaps they lead to water, perhaps they flee in terror.
@galev_ph The hallway gets more and more thickly covered in sticky webs towards the end.
@Iron_Fox off of the main foyer is an incongruous ball pit.