I checked in with my son about that area, as it's something I never came close to finding or accomplishing - he says that he's amazed that people have even found it, and that there isn't anything as special there as one would hope. I can't say much more as I've never seen it. He does seem sincere that there isn't anything there other than the fact that you found it. Sorry to disappoint! Hopefully you've gotten some pleasure from the rest of the game.
Oh, he just appended his conversation, and says there is a reason for that area in the whole lore of No Anglerfish, but that's a whole 'nother story.