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Kamikitayama Onsen is a hot spring town in Nara, Japan. The water leaves the ground at 35°C, comfortably warm. It measures pH 8.3 — mildly alkaline, the slippery kind. Officially the water is classed as bicarbonate spring.
Smooth, slightly slippery water. Often nicknamed bihada-no-yu, the water for beautiful skin.
Figures from the town's Japanese Wikipedia article.
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.