Akakura Onsen’s history stretches back more than 200 years, officially opening in 1816. The spring water contains calcium, magnesium, sodium sulfate and bicarbonate, excellent for wounds, circulatory disorders, depression, dry skin, etc. It also is well known for helping create beautiful skin.

The water comes from Kita Jigokudani ("north hell valley") high up on the north side of Mt. Myoko. The source has an impressive flow of 3,400 liters per minute, or some 5,000 tons of water every day. That flow means that the inns of Akakura can directly use the water in their baths and ensure hygienic conditions.

The water also arrives at almost the ideal temperature, at about 42°C. The sources at Kita Jigokudani come out at 40° to 60°, so that the water at the collection point on the mountain is about 50°. After traveling in pipes for several kilometers down the mountain, the water arrives at the hotels at about 48°; when it is actually in the baths it will be about 42°, with some variation by season. This means the water does not have to be either reheated or cooled down with cold water, with a volume that means the water is constantly replenished and remains fresh.

You may notice black or white materials in the water; these are known as yunohana, or "onsen flowers." This unique phenomenon is a sign of the excellent mineral content of the water. Some inns, in fact, allow the yunohana to build up over time; it may look like the water is dirty, but in fact it’s full of healthful materials.