Kawayu Onsen Wakayama

Kawayu Onsen in Hongu, Wakayama Prefecture, is a remarkable natural hot spring where thermal waters flow directly up through the gravel bed of the Ōtorii River, allowing bathers to dig their own temporary riverside onsen pools in the warm river gravel — one of Japan's most unusual and celebrated DIY hot spring experiences. In winter, the entire river is dammed to create the massive Senninburo or Bath of a Thousand People, a seasonal communal hot spring pool covering the entire river width where hundreds of bathers can soak together in the open air amid misty winter forest. Located on the sacred Kumano Kodo pilgrimage route in the ancient cedar and cypress forests of the Kii Peninsula, Kawayu Onsen embodies the animistic reverence for natural thermal waters at the heart of Japanese onsen culture and Kumano Shinto spirituality.