Ryūga Onsen is a hot spring town in Kochi, Japan. The water leaves the ground at 23°C, cool enough that the baths here are usually reheated. It measures pH 9.4 — strongly alkaline. Officially the water is classed as simple spring. 1 inns take visitors here.
Mild and low in dissolved minerals. Usually clear and gentle on the skin, which is why these baths are often recommended for first-timers.
Figures from the town's Japanese Wikipedia article.
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.