Explore the rooms if you want, and make note of the colorful stones on the wall in one of them.
Go up the stairs and through the middle door. Go through the tile maze (from the entrance: up, up, right) and press the switch at the end to disable the tiles.
In the next room, try to open the far door, then let yourself be caught. Keep refusing to eat the food.
Pick up the memo in the entryway. Continue past where you encountered the Sandman.
In the left room, get the note from the wall. Go to the right room and talk to Lullaby, then show them the memo and the notice to have them read.
Go through the room of fire-breathing statues. (For the last ones, note how the flames come out six times, then there's a break.) Pull the lever in the next room to disable them.
Navigate through the maze of clear glass walls. Your goal is the left door, not the stairs in the middle, and there are no forks in the path. Get the red bottle in the next room and use it in the maze room to mark the path.
Enter the code to open the door on the left.