The Legend of Zelda: The Wind Waker -
Once you arrive at Bomb Island, use a Bomb to blow up the large boulder, revealing an underground cavern. Drop down into the cavern and you'll find a locked door. If you step on the switch nearby it will open, but it will close as soon as you step off. Defeat the nearby Magtail and then place its body on the switch to hold it on. Walk on through to the next room.