There are spoilers in my comment, but I can't find a way to hide them
So, at first I was completely lost. Then I read all the spoilers, did as I was intended to, and still was lost. Line about treasures caught my attention - but I didn't figure out, what are they like, or even how does sonar work (I got low-pitched result, moved a bit forward, and sound was high-pitched again...). This - with all the difficulty of finding my way only based only on collisions in 3d - left me trapped in a cave with no clue about what should I do. I, the treasure hunter, would like to see some tutorial on using sonar (at least like a first treasure generated really close), and some clue on where cave's exit is (I imagine it as constant whale's noises, that are coming from exit direction when you are in cave). But I've read your devlog and played other games you made, and I see that you are focused on atmosphere rather than gameplay, and these simplifications could, maybe, go against realistic feeling you are trying to make. Also I love that theme "secrets of depth" and how you are keeping them even in your devlog :)