Ryûtan ("dragon depths") is a pond located near Shuri castle, the Ryukyuan royal palace.
It was designed by Chinese-born Ryukyuan official Kaiki during the reign of King Shô Hashi, and collects water from the "zuisen" pure water spring at the palace. When Chinese investiture envoys were resident on the island, they would celebrate Chrysanthemum Festival with boats on the pond, while members of the court performed music and dances.