Here's how you do it:
- Beat the game. The glitch is in the Destiny Islands portion of End of the World where you fight the first round of the final boss battles.
- As soon as Haley Joel Osment says "Is this, is this my island?" run directly behind you and jump onto the wooden shack. Going near the shore (or was it the hidden cove?) will trigger a cutscene.
- On the wooden shack, go to the far right corner of the roof and start jumping around.
- Eventually, you should have landed Sora on an invisible platform.
- Spam the jump button and watch as Sora crab walks to the heavens!
- Keep jumping until you're above the trees then head towards them. This insures that you will not fall back into the game's boundaries.
- You are now free to traverse the empty world of Destiny Islands. Not much to do really but mess around behind the island and to see how far away from the island you can get.
It's definitely a neat little trick to do and just proves I played this game too much when I was 10. I mean look at how high I got Donald's magic . . . seriously?