Diamond Steppe Island

Sail up close to the island and use your Hookshot on the bottom palm tree to get on top of the cliff. Drop into the hole.

This hidden cave houses some old shipwrecks -- and 15 warp cauldrons. If you don't know which ones to use, you'll be wasting a lot of time here. Basically, it's all trial and error, but here's a little map for you to help you through:

Jump into the cauldron and warp to the next area (red circle, marked 1). Go around the corner and defeat a hand. Take a stick and use it to light the lid of the cauldron marked "A". You may also just smash the lid with the skull hammer. Jump inside and warp to the first treasure chest. Open it to get a Joy Pendant. Hop back into the pot and burn this cauldron's lid next (below, right).

In the next area, walk forward and burn the right cauldron's lid (image below, left). Watch out for the hands. Hop into the pot. Your final cauldron to liberate (and use) is the one diagonally across from the one you came through (below, right).

Open up the treasure chest to get the Ghost Ship Chart. This handy little map lets you know where you can find (and enter) the mysterious ghost ship.