Near Banyuwangi and Bondowoso, this is a spectacular area of volcanic activity. The Ijen Plateau is the centerpoint of the large mountain range west of Banyuwangi, and which abouts 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 4x4) 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.
Two Road to the Ijen Crater
To the crater there are two roads: 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 (August 2017). The Banyuwangi approach is shorter, the Bondowoso approach gives you much better views.
The entrance to the volcano trail and the ticket office open at 1:00 AM. It will take you about 30 minutes to get the ticket as the guides mob the entrance to the ticket booth. This makes it rather challenging to see the blue flames of the sulfur fire inside the crater because daylight begins to break around 4:30 AM leaving you only about an hour to get to the top of the volcano and descend into the crater. The hike is 3 kilometers of constant uphill. With dedication and some sweat it is possible to complete it in under an hour. Consider carrying additional layers with you and only putting them on as needed at the top. You will get very warm very fast as you begin your ascend.
A headlamp, warm clothes, sturdy shoes, and a gas mask are absolutely required to visit the crater at sunrise. A nice optional addition would be ski goggles to prevent burning sensations in eyes from the intense sulfur clouds. Gas masks can be rented at the entrance to Ijen Crater, and make sure that it works and you can breath easily through it. Some of the masks handed out are clogged and difficult to breathe through. 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.