Formed by a series of eruptions some 3,500 years ago, Kawah Ijen is a massive volcanic crater located on a plateau between three towering volcanoes towards the very eastern tip of Java. To the east the plateau is backed by Gunung Ijen and Gunung Merapi with Gunung Raung to the far southwest.
Kawah Ijen is famous both for its acidic aquamarine lake and for the laborious sulphur mining industry which is played out beside the lake. Men from all around the region come here to mine sulphur with the resulting haul transported in bamboo baskets weighing up to 115 kilograms slung over their shoulders to waiting trucks. The trek out of the crater is gruelling with an ascent of 300 metres up one side and a descent of 400 metres down the other along a three kilometre track to Pos Paltuding.
The trail both the labourers and travellers follow is steep, gravelly and slippery. The trail quality, when combined with the swirling sulphur fumes and clouds, can be overpowering and excessive care (and a guide) is recommended.