蛇の湯温泉 is a hot spring town in Tokyo, Japan. It measures pH 10.5 — strongly alkaline. Officially the water is classed as simple spring and sulfur 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.
The classic rotten-egg smell and milky white water. It can tarnish silver jewellery, so take it off.
Figures from the town's Japanese Wikipedia article.
35.7260, 139.0497 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.