Tsurugadai Charanke Chashi was a fort constructed by ancestors of the Ainu, Japan’s native people. It is a designated National Historic Site. “Charanke” means “a conference” and “Chashi” means “a fort” in the Ainu language. However, although this place had been considered as a holy island (“tomosiri” in the Ainu) where “tokorokamuy” (the god of the lake) had a relaxing time, the Ainu people themselves had not known that there was a fort at this place until it was discovered in 1916. Thus the name was presumably given by the people from the mainland at that time. The chashi was in elliptical shape with 30 m from east to west and 18 m from north to south and enclosed by double moats. The place used to be an island in the lake, but is connected to the surrounding land now. This is an ancient Ainu sanctuary lost in oblivion.