They are then able to use it to recover explosives from Castle Cornelia to give to the dwarves so that they may gain access to Melmond. Other rooms opened by this key generally contain treasure chests with powerful weapons or armor for that point in the game, or large amounts of gil. Rooms opened by the Mystic Key can be found in Castle Cornelia, the Chaos Shrine, the Western Keep, the Marsh Cave, the Elven Castle, and Mount Duergar.