
Photo: 撮影:投稿者 (妖精書士) · CC BY-SA 3.0 · Wikimedia Commons
Saitama Seikawadera Onsen is a hot spring town in Saitama, Japan. The water leaves the ground at 38.3°C, comfortably warm. It measures pH 7.71 — mildly alkaline, the slippery kind. Officially the water is classed as chloride spring. Its sources put out around 380 litres a minute.
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.
35.9337, 139.5821 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.