In the space of eight minutes you go from a height of 741m to one of 1 044m to discover "Hell Valley": Owaku-dani. The valley came into existence 3 000 years ago, when a volcanic explosion ripped through the Kamiyama mountain (1 438m). The eruption left its mark on the ravaged, bronze-coloured landscape, which is dotted with fumaroles and where rock transformed into clay emits the stench of hydrogen sulphide. You can sample the blackened eggs (kuro tamago), which are cooked by being plunged into the boiling hot springs.