Sanjo-no-yu

Sanjo-no-yu is the only hot-spring mountain hut in the Oku-Chichibu range, standing alone at 1,103 metres on the flank of Mt. Kumotori in Tabayama Village, Yamanashi. It sits beside the Ushiroyama River, one of the headwaters of the Tama River, and can only be reached on foot because the drivable road ends far below. Local lore traces the spring back some 200 years, to a hunter who found a wounded deer healing itself in the warm water. The hut itself opened in 1950 and has been run by three generations of the same family for more than seventy years.

The water is classified as a simple sulphur cold mineral spring, emerging at about 10.5C with a strongly alkaline pH of 10.3 and a modest yield of four litres per minute. Clear and faintly sulphurous, it is heated with kerosene and firewood before filling the tub. Bathers describe noticeably smooth skin afterwards, and in midwinter, when the spring slows, the hut sometimes heats stream water instead.

There is only an indoor bath, separated by gender when the hut is busy and used in alternating time slots when it is quiet. Soap and shampoo are prohibited because waste water drains straight into the river. An overnight stay with two meals costs 11,000 yen, tent sites are also available, and both require advance booking. Day-use bathing costs 1,000 yen for adults and 800 yen for elementary school children, with the bath closing at 20:30.