Unknown Dungeon

The Unknown Dungeon is a very small cave in southern Kalos that can be accessed from Pokémon Village. A sole Mewtwo resides in the center with either the Mewtwonite X or Mewtwonite Y. The Unknown Dungeon is only accessible to Trainers who enter the Hall of Fame. Surf is needed to access the cave. Its purpose as a place to catch Mewtwo is a direct reference to Cerulean Cave in Kanto. It also shares its name with the alternative moniker for Cerulean Cave used in Japanese releases of the Generation I games.