An open-air bath on the shore of Lake Kussharo. Known as a hidden hot spring, Kotan no Yu features a stone-built bathtub facing the vast lake. It is kept very clean by local residents.

Separate changing rooms for men and women are provided, so you can change with peace of mind. However, while a large rock in the middle separates the men's and women's sides, the bathtub is essentially mixed bathing. Therefore, wearing a swimsuit or wrapping a towel around yourself is permitted.

The water level of the bath is almost the same as the lake's surface. In winter, swans float right before your eyes, making it feel as if you are bathing with them. Additionally, the beauty at twilight, when the lake is dyed in gold, is breathtaking for all to see.

Kotan Onsen has been featured in numerous magazines and television programs. It is a spectacular open-air bath that you should definitely experience at least once.