Shionosawa Onsen (Gunma)
- Location
- Saku, Nagano, Japan
- Water type
- sodium chloride
- Temperature
- 40 °C
- pH
- 7.3
Water profile
Relaxing — deep, immediate muscle release.
Loaded with major ions — the essential minerals (Ca, Mg).
Dense, salty water — you float without effort.
Shionosawa Onsen is a hot spring in Gunma Prefecture, in the thermally active mountain zone of this exceptional hot spring prefecture, whose sulfated mineral waters provide the joint-supporting and circulatory benefits characteristic of calcium and sodium sulfate springs in the volcanic highlands of the Kanto hinterland. Gunma Prefecture, enclosed by the Mikuni, Kanto, and Akaishi mountain ranges and drained by the Tone River system, is one of Japan's most productive hot spring prefectures, and the diverse sulfated springs distributed across its mountain valleys represent an important dimension of the thermal heritage that has made Gunma a destination for therapeutic bathing since ancient times. The mineral character of Shionosawa Onsen's sulfated waters reflects the specific geological context of its Gunma mountain setting, where the interaction of thermal water with sulfate-bearing rock formations produces the mineral composition that defines this spring type within the Japanese hot spring classification system.