Manganji Onsen Kawayu

Kawayu is a communal open-air hot spring bath set directly beside the Manganji River in the Shizu district of Minamioguni, Aso, Kumamoto Prefecture. According to the town of Minamioguni, Manganji Onsen is said to have been opened in 848 by the monk Kobo Daishi, and the open-air Kawayu bath was later built for the use of local residents. The village sits in a quiet mountain valley about ten minutes by car from the well-known Kurokawa Onsen, with hot water bubbling up at many points along the riverbank.

The water is an alkaline simple spring, colourless, odourless and tasteless, delivered as pure free-flowing spring water with no recirculation. It runs on the cool side, making long soaks comfortable. The bath is little more than a concrete-walled pool built around the spring where it rises in the riverbed, and its surface sits at almost exactly the same level as the river itself.

There is a single mixed-gender open-air pool. Changing facilities consist of an unstaffed, uncovered rack of shelves outdoors; there are no lockers, showers, or amenities of any kind. Bathing is possible around the clock, and visitors place a 200-yen contribution in the honesty box on site. Immediately beside the pool is a washing area where residents rinse rice and vegetables, so the bath remains woven into everyday village life.