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ヌプントムラウシ温泉 is a hot spring town in Hokkaido, Japan. The water leaves the ground at 91.9°C, hot enough that it has to be cooled before anyone can get in. It measures pH 9.1 — strongly alkaline. Officially the water is classed as chloride spring, bicarbonate spring and sulfur spring. Its sources put out around 88 litres a minute.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Smooth, slightly slippery water. Often nicknamed bihada-no-yu, the water for beautiful skin.
The classic rotten-egg smell and milky white water. It can tarnish silver jewellery, so take it off.
Figures from the town's Japanese Wikipedia article.
43.4911, 142.9583 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.