Senni Onsen
- Location
- Senni, Nagano, Japan
- Water type
- bicarbonate, carbonated
- Temperature
- 38 °C
- pH
- 6.3
Water profile
Soothing — neither hot nor cold, perfect balance.
Loaded with major ions — the essential minerals (Ca, Mg).
Mineralised water — eases movement and joints.
Senni Onsen in Nagano Prefecture carries a name evocative of the Japanese mystical tradition of sennin—immortal hermits who, according to legend, achieved transcendence through mountain asceticism, herbal medicine, and the consumption of pure mountain spring water, inhabiting the wild high places where thermal springs emerge from volcanic earth as expressions of the earth's inner vitality. The bicarbonate and carbonated waters deliver an effervescent, skin-stimulating mineral soak in which the natural CO2 provides lively animation to the gentle alkaline warmth—a spring whose effervescent character mirrors the animated, vital quality associated with the sennin's immortal mountain existence. This Nagano spring's hermit-immortal name places thermal bathing within the most ancient Japanese tradition of mountain retreat and mineral water as the path to extended life and spiritual transcendence.