Ijen plateau located near Banyuwangi, this is a spectacular area of volcanic activity. The Ijen Plateau is the center point of the large mountain range west of Banyuwangi, and which abuts the Baluran National Park to the north. Sights at the Ijen Crater include 1) bright blue flames from burning sulfur gasses seen only in the dark, 2) sulfur vents spewing yellow liquid molten sulfur which is collected and hauled out by miners, and 3) the warm acidic aqua blue lake that fills the crater.
The Ijen Crater (Kawah Ijen) can be approached from Bondowoso in the west or Banyuwangi in the east. From Bondowoso you are best off finding a guide with a car (preferably a 4×4) who will drive you through the village of Wonosari and eastwards up a very basic pot-holed road which winds its way up the mountain. You will pass through native casuarina forest and extensive coffee plantations before the road ends at the village of Jampit where there is some shelter available (Pos Paltuding). If you are travelling late in the day, you could actually bed down with a sleeping bag or camp here as you could in the disused volcanology station huts slightly further up the mountain.
The crater lake is a 90 minute hike further on from here. When you arrive the colour of the water in the lake is scarcely believable being an extraordinary vivid aqua blue. Evidence of volcanic activity is everywhere with steaming water and brilliant yellow crystalline sulphur deposits. Collecting the latter is an industry here and one with extremely harsh working conditions. You will see many workers trudging up and down the mountain carrying sacks of sulphur.
Getting to the crater there are two accessible routes: one from Banyuwangi and the other from Bondowoso. Both come together at Pos Paltuding, from where you can go up to the crater. The road from Bondowoso is in good shape, the road from Banyuwangi is not. It is steep and winding with many sections with loose gravel and poorly repaired holes.
The trek to the crater before sunrise can be quite dangerous with the toxic sulfur gasses and difficult walking terrain in the dark, and hiring a guide makes the experience a lot easier. Do not attempt this trek without a gas mask because the wind at the crater can change quickly and send thick sulfur clouds in your direction for long periods of time.