Atlantis

Atlantis (跡乱丁酢, Atoranchōsu, アイランドのちずちょう; lit. "Island of Atlas") is a state sized city build on an unusually large island which was once a part of Vanaheimr; the great Northern sub-continent of Naraka. Also known as the Fallen City (落ちた市街, Ochimashita Shigai), Atlantis sank into the depths of the ocean due to an unknown incident; suspected to be a tsunami, about 20,000 years ago.