筑後川温泉 is a hot spring town in Fukuoka, Japan. The water leaves the ground at 34–40°C, comfortably warm. Officially the water is classed as sulfur spring and radioactive spring.
The classic rotten-egg smell and milky white water. It can tarnish silver jewellery, so take it off.
Contains trace radon that leaves the water quickly. Also called radium or radon springs.
Figures from the town's Japanese Wikipedia article.
33.3588, 130.8077 — open the map
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.