Muraoka Onsen is a hot spring town in Hyogo, Japan. The water leaves the ground at 41.6°C, comfortably warm. Officially the water is classed as simple spring. Its sources put out around 250 litres a minute.
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.
35.4766, 134.5877 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.