Boing.

Description
This is a well-known glitch in Super Mario Sunshine. First, go to Gelato Beach. You have to enter on Red Coins in the Coral Reef. Hatch the Yoshi, and run over to the Dune Bud covered by the firey stuff. Spray it off, and dismount Yoshi. Here comes the tricky part. Spray the Dune Bud, and pound. You have to time your pound so that you hit at the exact moment the sand caves in. Be sure to release L immediately, or it won't work. As you collide, the screen will show the sky with a little speck in it. The screen will slowly scroll down, then will spaz out. You should feel the controller rumble (if you have rumble on). Then, you will see a high-up view of Isle Delfino. It will quickly zoom in, and Mario will be standing right next to the Dune Bud.

Credit
Several videos of this glitch were found on Google Video and Youtube.