Teraono Onsen Yakushi-yu

Yakushi-yu is a communal bathhouse in the hamlet of Teraono in Oguni, Aso District, Kumamoto Prefecture, on the western foot of Mount Waita. A single small wooden bathhouse stands at the bottom of a slope surrounded by terraced rice paddies and cedar forest, and because there is almost no signage, first-time visitors must follow narrow village lanes and a footpath between the paddies. The bath has been maintained by an association of Teraono residents, and the names of those who donated toward its construction are still listed inside. Named after Yakushi Nyorai, the Buddha of healing, it is widely regarded among Japanese hot spring enthusiasts as one of Kyushu's essential hidden baths.

An old analysis notice posted in the bathhouse records the water as a hydrogen sulfide spring, with a discharge of 34.4 litres per minute. The water is colourless and clear, with a faint egg-like taste, a slight bitterness and a mild sulphur aroma. It emerges at around 40 to 41 degrees Celsius, cool enough to soak in for a long time without overheating. The bath is pure free-flowing spring water with no heating, no dilution and no recirculation, constantly overflowing the rim of the tub. The pH and total mineral content are not posted and remain unknown.

There is one small indoor bath each for men and women, in a plain room where the changing area and the bathing area are not separated. Each bath is divided into two sections, with water entering at the far end and flowing toward the near end, so the near section is noticeably cooler. There is no reception and no attendant: bathers drop 100 yen for adults and 50 yen for children into an offering box in the changing room, and the bath can be used at any hour as long as the door is open. There is no dedicated car park, so visitors leave their car near the sign at the hamlet entrance and walk down. Note that as of August 2026 the bath is reported to be temporarily closed because of a decline in the spring's flow.