Kawayu Onsen

Kawayu Onsen is a hot spring village in the mountainous interior of Wakayama Prefecture, deep within the sacred Kumano region. What makes Kawayu unique is its river — the Oto River's gravel bed is naturally heated by underground volcanic activity, allowing bathers to dig their own onsen right in the riverbank and soak under open sky.

In winter, the village constructs the massive Sennin-buro, a giant open-air bath formed by damming a section of the river to create a communal hot spring large enough for a thousand bathers. Surrounded by forested mountains and the spiritual atmosphere of the Kumano Kodo pilgrimage routes, Kawayu offers an onsen experience unlike anything else in Japan — raw, natural, and deeply connected to the landscape.