Shibu Goten-yu Onsen is a hot spring town in Nagano, Japan. The water leaves the ground at 27°C, cool enough that the baths here are usually reheated. Officially the water is classed as acidic spring and sulfur spring. 1 inns take visitors here.
Strongly acidic, sometimes below pH 2. It stings on cuts and is not for long soaks.
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.
36.0361, 138.3294 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.