Rich in active gases or metals — a strong mineral character.
Buoyancy
Standard buoyancy
LowHigh
Soft water — natural, classic buoyancy.
SoufreSulfuresSulfates
Yu no Koya Onsen Yumotokan, an onsen in Minakami, Gunma, offers a soak in thermal sulfurous water at 46°C, alongside an outdoor bath (rotenburo) and a sauna.
Insider tip — 'Yu no Koya' (hot spring hut) at Yumotokan in Minakami — one of the great onsen towns of the Japanese Alps, where the Tone river begins its descent to Tokyo Bay. The volcanic Shirane Mountains above supply consistently sulfurous waters. Minakami is also Japan's rafting capital and the start of the Tone river's famous whitewater.