Rock Spire Isle

This is a long slender island with the path to a secret cave being blocked by rocks. To destroy the rocks, one needs a couple of Bombs and good timing. Blow up the rocks and enter the cave, use your stick to light up the room and destroy all the Keese. Once the last one is destroyed, you will a chest will appear leading to 200 rupees.

There is a somewhat different kind of Beedle shop here called "Masked Beedle" where they sell otherwise unbuyable items. You can purchase a Piece of Heart, Empty Bottle and Treasure Chart here.