Successfully complete the game and watch the ending. Return to the gate and examine the "stuff". Leave and the Final Dungeon will be selectable again.

Successfully complete the game and watch the ending. Display the world map and the secret "River Belle" dungeon will be unlocked at the lower right part.

Successfully complete the game under the Hard difficulty setting to unlock the following items for purchase at the shop for 1 million gil each:

Hairpin of Affection
Layle's Goggles
Layle's Jacket
Parallel World Garb
Robot Body
Robot Head