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Yachigashira Onsen is a hot spring town in Hokkaido, Japan. The water leaves the ground at 65.1°C, hot. It measures pH 6.4 — close to neutral. Officially the water is classed as chloride spring. Its sources put out around 330 litres a minute.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Figures from the town's Japanese Wikipedia article.
41.7519, 140.7142 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.