Ōtaki Onsen is a hot spring town in Saitama, Japan. The water leaves the ground at 33.1°C, cool enough that the baths here are usually reheated. It measures pH 8.4 — 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.
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.