Nation-leading therapeutic hot-spring effects! A Showa-retro radon onsen
Yamanashi Kai City
A hot spring facility that has preserved its Showa-era retro charm since opening in 1980 (Showa 55). You can enjoy high-quality natural hot spring water selected as one of Yamanashi's 100 Famous Hot Springs, provided as 100% free-flowing from the source with no added water or reheating. Its standout feature is the radon inhalation room, which uses a medical-grade radon generator. In a sealed space, soaking in the hot spring while inhaling radon gas is expected to produce an extraordinary sweat-inducing and detoxifying effect, even surpassing a sauna.
TypeNatural Hot Spring
A sodium-chloride and bicarbonate spring sourced from 1,000 meters underground, offered as 100% free-flowing from the source with no circulation, dilution, or reheating. The slightly amber-tinted water feels smooth on the skin and boasts strong therapeutic hot-spring effects.
Sauna TypeSteam Sauna
Capacity12people
A unique steam-sauna-like space with a bathtub inside. High-concentration radon gas delivered from the radon generator is absorbed through breathing and the skin, promoting intense sweating that can surpass a typical sauna.
Water Qualitynatural_spring
Capacity4people
A cold plunge bath located just outside the radon inhalation room. Water quietly flows through gaps in the tiles, gently cooling a body that has been heated to its limit by the radon bath.
Closed Days: None
〒400-0113 1300-1 Tomitake Shinden, Kai City, Yamanashi Prefecture, Japan
Gender Access
Gender Separated
Curated by an expert who visits onsen and sauna facilities every day and has explored 300+ locations — only facilities confirmed to be truly exceptional are featured.
Learn more
Nation-leading therapeutic hot-spring effects! A Showa-retro radon onsen
Yamanashi Kai City
A hot spring facility that has preserved its Showa-era retro charm since opening in 1980 (Showa 55). You can enjoy high-quality natural hot spring water selected as one of Yamanashi's 100 Famous Hot Springs, provided as 100% free-flowing from the source with no added water or reheating. Its standout feature is the radon inhalation room, which uses a medical-grade radon generator. In a sealed space, soaking in the hot spring while inhaling radon gas is expected to produce an extraordinary sweat-inducing and detoxifying effect, even surpassing a sauna.
TypeNatural Hot Spring
A sodium-chloride and bicarbonate spring sourced from 1,000 meters underground, offered as 100% free-flowing from the source with no circulation, dilution, or reheating. The slightly amber-tinted water feels smooth on the skin and boasts strong therapeutic hot-spring effects.
Sauna TypeSteam Sauna
Capacity12people
A unique steam-sauna-like space with a bathtub inside. High-concentration radon gas delivered from the radon generator is absorbed through breathing and the skin, promoting intense sweating that can surpass a typical sauna.
Water Qualitynatural_spring
Capacity4people
A cold plunge bath located just outside the radon inhalation room. Water quietly flows through gaps in the tiles, gently cooling a body that has been heated to its limit by the radon bath.
Closed Days: None
〒400-0113 1300-1 Tomitake Shinden, Kai City, Yamanashi Prefecture, Japan
Gender Access
Gender Separated
Curated by an expert who visits onsen and sauna facilities every day and has explored 300+ locations — only facilities confirmed to be truly exceptional are featured.
Learn more