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桜野温泉 is a hot spring town in Hokkaido, Japan. The water leaves the ground at 55.5°C, hot. It measures pH 7 — close to neutral. Officially the water is classed as chloride spring.
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.
42.1480, 140.2901 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.