Masutomi no Yu
Masutomi, Yamanashi, Japan
- Location
- Masutomi, Yamanashi, Japan
- Water type
- radioactive
- Temperature
- 30 °C
- pH
- 7.3
Water profile
Thermicity
Invigorating
LowHigh
Stimulating — wakes the body and boosts circulation.
Mineralisation
Bio-active
LowHigh
Rich in active gases or metals — a strong mineral character.
Buoyancy
Standard buoyancy
LowHigh
Soft water — natural, classic buoyancy.
RadonLithiumBicarbonates
Masutomi no Yu, in the village of Masutomi, Yamanashi prefecture, is known for its naturally radioactive water, cooler at 30°C (pH 7.3) than most onsen in the area. An indoor bath, an outdoor rotenburo and a sauna complete the facilities.
Insider tip — Masutomi is Japan's most celebrated radium spring, a naturally cold water emerging at 30°C from the Kamanashi River gorge that has attracted visitors since the Meiji era. The high radon content and cold temperature — unusual among onsen — deliver a uniquely invigorating bathing experience. The surrounding gorge scenery is dramatic, making the journey to the spring as memorable as the soak itself.
Nearby
Frequently asked questions
How hot is the water?
The water is on the cooler side here, around 30 °C — an invigorating water that boosts circulation.
What type of water is found here?
This spot features radioactive water.
What is the best season to visit?
The most favourable period for this spot is: Toute l'année.