The game must already have been completed in order for this to work. Right at the end of the game when Ico wakes up on the beach, make your way all the way over to where the cliffs are and continue your way up the beach. Along the way you should come across a large rock, there should also be a couple of watermelons situated near this large rock. Pick up one of these watermelons and proceed up the beach until you reach Yorda. You will now be treated with a slightly humurous end video. This does not work on the US version of the game.