The Sunken Cave, also known as Underwater Cave, is an optional dungeon in Final Fantasy III. It is located underwater the small island to the extreme southeast of the Surface World, so the party will need the Nautilus that can use its feature to dive into the underwater surface. The Sunken Cave has a wealth of chests containing lots of equipment and a few items. At the end, there is a mass of rock and bridge that may hint that there was much more of the cave previously.