An open-air bath on the shore of Lake Kussharo. Kotan's Bath, known as a secret hot spring, is a stone-built bathtub facing a spacious lake. Cleaning by local people is thorough, and it is very clean.

Since gender-separated changing rooms are also provided, doing changing clothes is also reassuring. However, as for the bathtub, a large rock in the middle separates men and women, but basically, it is synonymous with mixed bathing. Therefore, wearing a swimsuit or bathing wrapped in a towel is also possible.

As for the bath's water surface, it is almost the same height as the lake surface. In winter, swans float in front of one's eyes, just as if one is mixed bathing with swans. Also, as for twilight when the lake is dyed golden, it is a beauty to the extent that everyone takes their breath away.

Kotan Onsen, which has been featured in numerous magazines and on television. It is a spectacular view open-air bath that one definitely wants to bathe in at least once.