日乃出温泉 is a hot spring town in Yamaguchi, Japan. The water leaves the ground at 19.2°C, cool enough that the baths here are usually reheated. It measures pH 7.9 — mildly alkaline, the slippery kind. 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.
33.9450, 130.9173 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.