Go east on the island and enter the cave. Go left, then north, and bomb the wall with the bombable spot.
Go through the maze, avoiding the Rupoors and killing the Keese. Rupoors look like black Rupees. If you hit one, you lose Rupees. Keese are bat-like monsters that are vulnerable to your bow. Exit the maze from the north side. Go to the stairs off to the right after looting the chest. Exit the cave.
Travel west, killing the Like-Like before heading north. Kill the second Like-Like on the northern path and then head east once it is dead. Like-Likes are amorphous blobs that suck you in their mouths, steal Rupees or shields, and then spits you out. Enter the pyramid.
Kill the Keese here and read the right-side tablet. Exit the pyramid and go southeast to the tip of the island, where the sacred tree is located. Go 13 squares west and seven squares north. Use your shovel to open the hidden hole.