Okay I had the same issue you are having. The middle is a trap only, there is nothing g there and no way to bypass him. If you got the invisibility shrine and the sword you need to go back outside and get onto the boat you arrived on. Then go to the gate at the top of the map to use the sword. There will be 4 more puzzles then you be able to get the dream corruption ability.Im stuck on a puzzle, anyone knows how to "solve" this?
(Yes i entered both rooms on the edges)
Update: got it, i needed to go back to the boat
*Edit*
I read your update after i posted this, congrats and my bad for not reading the whole post.