Shimogamo Onsen is a hot spring town in Shizuoka, Japan. The water leaves the ground at 70°C, hot. Officially the water is classed as chloride spring.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Figures from the town's Japanese Wikipedia article.
34.6500, 138.8500 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.