The Oyunuma Pond is the crater of the bursting crater formed by the fire in the Japanese and the mountain. The sulphur spring of about 130 degrees is sprayed at the bottom of the pond. It is the source of hot spring water for the local hot spring hotels. A circle around the lake, in addition to smelling the sulphur smell, you can also see the source of hot spring foaming at any time, especially the floating yellow spheroidal sulfur on the lake is particularly conspicuous. There is also a natural foot bath next to the Oyunuma Pond.