To the east of Nagasaki, Unzen Onsen is a hot spring resort that became a popular resort for local and foreign visitors in the Meiji period (1868-1912), when Nagasaki's foreign settlement was established. But the nearby Unzen Hells (Unzen Jigoku), an area of volcanic activity where steam and hot sulfurous gasses spurt from the ground, has an entirely different history. Christian martyrs were killed here between 1627 and 1632. Today there is a monument at Oito Hell to remember those who died here. You can follow a winding path through about 30 hellish bubbling pools, dotted amongst steaming fields of white clay, formed by heat and the acidic waters. At the end of the path there is a free hot spring foot bath and a shop selling refreshments and souvenirs.
Unzen-shi, Nagasaki 854-0621