Ryugu
Ryūgū-jō or Ryūgū is the supernatural undersea palace of Ryūjin or Dragon God in Japanese tradition. It is best known as the place in fairytale where Urashima Tarō was invited after saving a turtle, where he was entertained by the Dragon God's princess Oto-hime and his minions, but when Urashima returned back to land after what he thought was a few days away, centuries had passed.