Azohara Onsen

Azohara Onsen is a hot spring in the Kurobe Gorge, in Kurobe, Toyama Prefecture, Japan. Its single open-air bath is a concrete pool set beside the portal of a tunnel of the Kansai Electric Power Kurobe Railway, about 5 to 10 minutes' walk down from Azohara Onsen Hut. The water is a simple thermal spring at 47.3°C, flowing naturally at 46.3 litres per minute.

The hot spring is fed by water heated in rock over 160°C during excavation of the Kanden tunnel for the Kurobe Senyō Railway; the tunnel still holds around 40°C. In January 1940 an avalanche destroyed a six-storey workers' dormitory at Azohara, killing many, and a fire followed. The Azohara Onsen hut was built on that site in 1949 for forestry workers and opened to hikers in 1965.

The bath is a single concrete open-air pool fed by water drawn from the nearby tunnel of the Kansai Electric Kurobe railway; bathers alternate by gender on a timetable posted at the hut and at the pool entrance, and from 20:00 the pool becomes mixed. The hut, open from July to October, charges non-guests a fee for the bath.

Access is on foot only: about 12 km via the horizontal trail from Kurobe Gorge Railway Keyakidaira Station, or about 19 km via the Nichiden trail from Kurobe Dam Station. Both are advanced mountain routes with danger, and the onsen is sometimes called Japan's most dangerous. The hut and bath operate from July to late October; after closing, the bath, toilets and water are unavailable.

The bath sits beside the portal of the tunnel dug for the Kanden tunnel; water comes from inside it. Rock heated above 160°C during excavation still holds around 40°C, warming the spring. The open-air tub is concrete, bathers alternate by sex on a posted timetable, and mixed bathing starts after 20:00.