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Niseko Yakushi Onsen is a hot spring town in Hokkaido, Japan. The water leaves the ground at 37–40°C, comfortably warm. Officially the water is classed as chloride spring and iron spring.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Turns reddish brown as the iron meets air. The water is clear at the source.
Figures from the town's Japanese Wikipedia article.
42.8331, 140.5939 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.