Go to Ganon's Castle and then hop off onto the dirt ledge at the right of the door. Take about 5 steps and turn towards the door. Now take out your Longshot and aim at the pillar that makes the door. You have to aim at the top and as far right as possible. If in the right position you will fall behind the wall. At first it will look like Link dissapeared, but press C-Up or Z and you will be able to see behind the wall, and walk on a hidden castle ledge. Nothing special just a cool glitch.