Sashiusudake Onsen
- Location
- Shirahama, Japan
- Water type
- carbonated
- Temperature
- 45 °C
- pH
- 3.5
Water profile
Relaxing — deep, immediate muscle release.
Loaded with major ions — the essential minerals (Ca, Mg).
Mineralised water — eases movement and joints.
Sashiusudake Onsen is found in the Shirahama area of Wakayama Prefecture, a celebrated coastal resort region on the southern Kii Peninsula long associated with refined leisure and the pleasures of the Pacific shoreline. Shirahama itself — famous for its white sand beach and concentration of historic onsen — draws visitors from Osaka and Kyoto seeking the combination of ocean scenery and geothermal bathing. Sashiusudake adds a more distinctive dimension, its waters emerging with a character quite unlike the region's milder springs.
The spring is a carbonated water at a comfortable 45 °C — warm enough to envelop the body immediately — and carries a notably acidic pH of 3.5, which produces a faintly tingling sensation on the skin characteristic of acid carbonated springs. The effervescent quality of the water can be perceived as small bubbles forming on the skin during longer soaks, a feature prized among onsen enthusiasts. This combination of warmth, acidity, and carbonation creates a bathing experience with a distinctive sharpness that contrasts with the gentle coastal atmosphere of the Shirahama coast.