There's no way to ask this elaborate question without both spoilers and sounding slightly like a crazy person, so I'm just going to go ahead.
I've gotten to a sort of second hidden portion of the game using the information from the secret ending. After the shark-man gives me the third key (Which the game informs me should work on most doors) and asks me to go to the basement, I am not able to find the entrance. All the doors are either non-interactive or still tell me they are locked. This includes the door in the fish-themed smaller gallery.
Is this a bug, was this portion of the game not finished, or am I just somehow missing the basement door? No worries if the game wasn't finished past this point, just hate to think I am missing something.