No secret dungeon, but face has a use! = )
Hi. There isn't a secret dungeon in this game, however the face on the moon near where the secret dungeon used to be does actually serve a purpose provided the correct situations are met. When fighting the final boss, Zeromus, there is an item you can steal off him called "Dark Matter" which will grant you access to fight the super-bosses, Geryon and Proto-Babil. To fight the Proto-Babil, you go up to the face on the moon and use the Dark Matter, be warned this is the STRONGEST SUPERBOSS IN THE GAME and it is recommended you completely max out your characters stats and gave access to the strongest equipment in the game such as Onion Swords and Shields, Ribbons or Glass Masks, ADAMANT ARMOUR is a must to save you from the attack, Ninth Dimension, which the Proto-Babil has a tendency to spam on you and Crystal Rings. For Edge, you'll want the Masamune and Murasame weapons, for Rosa having the Artemis Bow is a great asset, but the Yoichi Bow still does the job, and for Rydia you'll want the Dragon Whisker weapon.
Added by: beastmachinebender Aug 21st 2010, ID#14543