Rich in active gases or metals — a strong mineral character.
Buoyancy
Standard buoyancy
LowHigh
Soft water — natural, classic buoyancy.
SoufreSulfuresSulfates
Koyabu Onsen flows with bicarbonate and sulfurous thermal waters in Ozu City, Ehime Prefecture on Shikoku Island, emerging from the geothermal depths beneath the Koyabu River which joins the Hijikawa River just downstream of the Kanogawa Dam. Set in the scenic river valleys of the former Iyo Province, the spring is accessed by following the Koyabu River upstream from its confluence with the Hijikawa, rewarding visitors with naturally carbonated alkaline waters amid lush forested hillsides. The dual-mineral chemistry of bicarbonate and sulfur produces waters prized for skin softening and circulatory benefits, making this a distinctive and therapeutic stop for travelers exploring rural Shikoku.
Insider tip — Koyabu Onsen is a secluded hot spring in the mountainous heart of Kochi Prefecture on Shikoku island, fed by bicarbonate-sulfurous waters bubbling up from deep volcanic fissures. The dual mineral character makes it particularly effective for muscle recovery and respiratory health according to traditional Japanese bathing medicine. The surrounding cedar and hinoki forests are ancient and cathedral-like, lending the soak a contemplative quality. Access requires a winding mountain road that rewards patient travelers with tranquility and wild nature.
