Shimojima Onsen Senyukan

A rare carbonated spring, said to be among roughly 0.5% of Japan's hot springs, flows naturally into the baths here beside a mountain stream. The mixed open-air bath (konyoku rotenburo, 混浴露天風呂) sits right at the edge of the river, and the water comes out at a gentle temperature perfect for long soaks. A small, unpretentious inn with an old-fashioned feel.