Mt. Io is also known as “Atosanupuri” which means “a naked mountain” in Ainu language. It is a mountain located inside Akan Mashu National Park. There are over 1,500 large and small craters in the park so people can constantly hear the  deep sound of white volcanic fumes erupting at there. Moreover, it is possible to observe yellow sulfur crystals and dynamic volcanic fumes up close and smell the distinctive sulfur smell in the area. It is very hot near fumaroles so visitors  need to be careful not to burn themselves. At the rest house, people can purchase and eat hot spring eggs cooked using geothermal heat.

There is a famous onsen called Kawayu Onsen located about 3km away from the mountain. It is an onsen of good spring quality which comes from Mt. Io. The best season to visit Mt. Io is from the middle to the end of June when Japanese Labrador Tea flowers bloom. It is also popular to visit during the autumn. An opportunity to walk in the nature and relief one’s stress by bathing in hot springs is what makes people to visit Kawayu Onsen and Mt. Io every year.