Doai Onsen is a hot spring town in Gifu, Japan. The water leaves the ground at 10.5°C, cool enough that the baths here are usually reheated. Officially the water is classed as carbon dioxide spring.
Fine bubbles cling to your skin. Rare in Japan, and usually cooler than other springs.
With tattoos
Many public baths still turn away visible tattoos, and the rule is set by each bath, not by the town. The reliable way round it is to bathe privately: a room with its own open-air bath, or an inn with a private bath you can book for yourselves.