Kawayu Onsen Sennin-buro River Bath

Sennin-buro ('bath of a thousand people') is created every winter, from December 1 to February 28, by damming a section of the Oto River, a tributary of the Kumano River, in Hongu-cho, Tanabe City. Hot spring water emerges from the riverbed at around 73°C and mixes with the cold river water to settle around 40°C in the pool, which typically measures about 40 by 15 meters and 60 centimeters deep, though its exact size varies year to year with the water level. Entry is free, requires no reservation, and swimwear is required; bathers can dig their own smaller pools directly into the gravel riverbed.