Super Mario 64 Glitches

Fall Into The Castle
When you`ve gotten all 120 stars, get the wing cap on the castle. Go to the cannon with it and blast off, aiming to land on the central tower where the roof part is (not quite the very top). Face the side of the tower that faces the front of the castle and jump at it. After a few tries you will jump throught and fall in. You will lose half of your health, but you will be in a void behind the door. If you go "out" the door, you will be in the void behind the inside door. To get out, make sure you can see the inside and you can walk through any part of the wall around the door.