In the forest level there is a well that you can jump down. I don't remember what turns to take but theres a room with four tombstones that is normally blocked by a metal bar gate, but if you press "J" the gate disappears. It also gets rid of the gate to the beating heart thing and the swinging blades.
Edit: I didn't know exactly what to call it, seeing as some of the keys effects start with the letter of the key (like "F" for fish, "G" for gravity etc.) so I went with jail door cause it kinda looks like prison bars.
