A very well-defined atmosphere of a subterranean and semi-submerged place, with sinister creatures, very Appendix N-style.
I liked the mechanics of getting lost, although I found it a bit confusing as I read the rest of the Adventure, but I still need to actually play the game to see the idea in action.
Overall, I really liked the idea and would like to see a more evocative, and well deseved cover for your creation.