The Ijen Plateau lies in the centre of the Ijen - Merapi - Maelang Reserve, which extends over much of the mountainous region to the west of Banyuwangi, bordering or, the Baluran National Park. A luminous blue/green crater lake which surface is streaked in wind-blown patterns of yellow sulphur lies at the far eastern end of the plateau and is without doubt one of the most impressive of East Java's natural wonders.

The lake can be reached from either the east or the west. The latter is the more popular approach, since it takes just an hour and a half to hike up the mountainside from the road's end. Ijen Crater is the world's largest highly acidic lake, which depth is 200 m and height is 2.300 m above the sea-level; it contains of approximately 36 millions cubic meter of steaming acid water, shrouded in a swirling sulphur cloud.

Sulphur is mined at the lake's edge and the average yield is nine to twelve tons per day. Experienced sulphur collectors, who are paid by weight, are able to transport loads of up to 90 kg to the top of the crater and then 17 km down the mountainside to Banyuwangi, mostly on foot. After arrival at the factory, the sulphur is treated for use in the production of medicines as well as for processing sugar.