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Aurora Onsen is a hot spring town in Hokkaido, Japan. The water leaves the ground at 43.6°C, hot. It measures pH 9.4 — strongly alkaline. Officially the water is classed as simple spring. Its sources put out around 94 litres a minute.
Mild and low in dissolved minerals. Usually clear and gentle on the skin, which is why these baths are often recommended for first-timers.
Figures from the town's Japanese Wikipedia article.
43.3252, 144.5274 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.