Sprugtooth was watching a documentary on the sinking of the Titanic and he thought of this classic trap. It's simple and sadistic: step near the trigger (needs a still room), the doors drop shut and water starts to fill the room. It takes 20 seconds to fill the whole room.
Detect: Per-based Traps at -2.
Disarm: DX-based Traps at -5.
Circumvent: Automatic (don't go into the room).
Evade: Hearing roll allows Dodge if he's standing in the doorway to jump to the other side.
Effects: Room floods in 20 seconds.