赤川温泉 is a hot spring town in Oita, Japan. The water leaves the ground at 26–28°C, cool enough that the baths here are usually reheated. It measures pH 4.9 — mildly acidic. Officially the water is classed as sulfate spring, carbon dioxide spring and sulfur spring. Its sources put out around 400 litres a minute.
Clear water with a faintly bitter taste. Known for holding heat.
Fine bubbles cling to your skin. Rare in Japan, and usually cooler than other springs.
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.
Planning a first soak? Read how an onsen stay works, and what to do if you have tattoos.