Yet another Dark World for Super Mario 64. Do do this one, Backwards Long Jump up the Endless Stairs, and if you do it at the right angle, you will fall through the wall, and fall down below the stairs on the third floor (the one with Wet-Dry World). I'm not sure if you can escape, so just try it.
Why it works Edit
You shoot through the wall, the DW is below where you fall.
Found on a glitch video.