Hot springs in Nakatsugawa

Rosoku Onsen, formally the Yunoshima Radium Mineral Spring Sanatorium (湯之島ラジウム鉱泉保養所), is a radium spring and cure-stay inn in the Takayama district of Nakatsugawa, in the mountains of Gifu Prefecture. The operator describes the water as among the richest in radium in Japan, drawn from several sources on an estate of about 80,000 tsubo (roughly 26 hectares) of forest with a mountain stream and walking paths. The spring is classed as a simple radioactive spring (単純放射能泉), and the operator cites a radon content of 2,020 × 10⁻¹⁰ curie (556 Mache units) measured by a Gifu Prefectural institute. The inn is built around toji, the traditional cure stay: bathing, drinking the water and breathing the radon-rich air, with gentle walks between soaks. Meals favour vegetables from the inn's own pesticide-free farm, river fish and mountain vegetables. Day visitors are welcome on the days the inn is open to them, which the operator publishes each month.