The Unknown Cave is a secret location in Final Fantasy V. It is a one-room cave with no monsters, and only one inhabitant, Mr. Clio. When talking to him, he can show the player their various stats, including number of battles fought, number of monsters slain, average Experience, percent of treasures looted, and number of times the game was saved.
The Unknown Cave is the only location in the merged world (besides Phantom Village) not to be indicated on the map with a blinking star, so it can be frustrating to locate at first. To find it, all the player must do is land the airship in the small sea directly south of Karnak and submerge. On the ocean floor, there will be a purple-colored rock with a hole in the middle. This is the entrance to the Unknown Cave.