1) Most likely human entrance from the surface.
2) cage area that blocks exit. Could be a secret door or two in these metal walls.
3) an innocent looking metal door and bones in the room.

4) Rubble blocks the path to 5. open on one side, drop off to sand down below. Did the sand just move ?
5) a cave-like area. Rubble blocks path to room 6.
6)  Loose rocks on floor

7) the water can be slow, or swift and sweep characters away Connects to The Ruins.
8) a cave area, the water is moving and can sweep a character off into the depths of sand.
9) a floating stone area that connects 7 and 8