Hot springs in Kusatsu

A radium mineral spring resort in a forested valley near Nakatsugawa, Gifu Prefecture. The spring contains the highest natural radium content of any hot spring in Japan. The surrounding 80,000-square-meter forested site is organically cultivated. The name rosoku means candle in Japanese, a reference to the way radon gas rises silently and invisibly from the spring, like the unseen burning of a flame.

One of Japan's most celebrated onsen towns, set at 1,200 meters in the mountains of Gunma Prefecture. The spring output here exceeds 32,000 liters per minute, making it the highest in Japan. The strongly acidic sulfur waters are legendary for their skin-healing properties. Twice a day in the town square, staff perform yumomi: cooling the scalding water with long wooden paddles while singing traditional songs.