Photo: 唐山健志郎 · Public domain · Wikimedia Commons
Futamata-Radium Onsen is a hot spring town in Hokkaido, Japan. The water leaves the ground at 43°C, hot. It measures pH 7.1 — close to neutral. Officially the water is classed as chloride spring and radioactive spring. 1 inns take visitors here.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Contains trace radon that leaves the water quickly. Also called radium or radon springs.
Figures from the town's Japanese Wikipedia article.
42.5767, 140.2393 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.