Photo: Alpsdake · CC BY-SA 4.0 · Wikimedia Commons
Nakabusa Onsen is a hot spring town in Nagano, Japan. The water leaves the ground at 56–97°C, hot enough that it has to be cooled before anyone can get in. Officially the water is classed as sulfur spring. Its sources put out around 770 litres a minute.
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.
36.3942, 137.7466 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.