真湯温泉 is a hot spring town in Iwate, Japan. The water leaves the ground at 56°C, hot. Officially the water is classed as sulfate spring and acidic spring.
Clear water with a faintly bitter taste. Known for holding heat.
Strongly acidic, sometimes below pH 2. It stings on cuts and is not for long soaks.
Figures from the town's Japanese Wikipedia article.
39.0000, 140.8500 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.