Rich in active gases or metals — a strong mineral character.
Buoyancy
Standard buoyancy
LowHigh
Soft water — natural, classic buoyancy.
SoufreSulfuresSulfates
Nagasaki Unzen Onsen Fukuya is located in the Unzen resort town on the Shimabara Peninsula in Nagasaki Prefecture, within Japan's first-ever National Park (designated 1934), centred on the dramatic Unzen volcanic massif whose billowing fumaroles and boiling mud pools — the infamous jigoku or 'hells' of Unzen — create one of Japan's most otherworldly volcanic landscapes. The intensely sulphurous thermal waters of Unzen, saturated with hydrogen sulphide from highly active fumarolic venting, have a sobering historical connection to the 17th-century persecution of Japanese Christians, when martyrs were tortured in the springs — a dimension of tragedy embedded in this beautiful volcanic resort's past. Fukuya's traditional inn brings together centuries of Unzen's onsen culture with the dramatic natural theatre of the Shimabara Peninsula's still-active volcano, which famously generated devastating pyroclastic flows in 1991.
Insider tip — Unzen Onsen sits atop the Shimabara Peninsula amid the Unzen-Amakusa National Park, where the jigoku — boiling hell vents — hiss and bubble in a lunar landscape of white sulfur-encrusted fumaroles. The 1991 pyroclastic flow from Mount Unzen caused Japan's deadliest volcanic disaster in the modern era, and the area still shows the raw power of the volcano in its steaming hillsides. The sharply sulfurous water in the ryokan baths turns metal fittings black within days. Stay in one of the historic hot-spring hotels that survived the eruption and soak in baths that have welcomed guests since the Meiji era.