Niseko Onsenkyō is a hot spring town in Hokkaido, Japan. Officially the water is classed as chloride spring, iron spring and sulfur spring.
Salty water. The salt leaves a thin film on the skin, so you stay warm well after leaving the bath.
Turns reddish brown as the iron meets air. The water is clear at the source.
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.
42.8000, 140.6800 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.