It is a volcanic lake with tosca green color in the altitude of 2,386 meters and has about 5,466 hectares of area.
A crater with caldera walls of 300 to 500 meters high has zero degree acid level and 200 meters of depth. Its strong acid degree is strong enough to melt clothes and human fingers. The volcanic lake water, which reaches 200 million3 and has 200占쏙옙 of temperature, is quite calm with bluish green color and looks so amazing especially in the morning producing golden green glow when the sun shines on the surface from behind Mt. Merapi, the twin of Mt. Ijen.
While we are at the edge of the crater and 2,400 meters high we can see a spectacular view: greenish lake with 1 km2 of diameter covered with fog and Sulphur cloud. The sulphur miners are part of the view. To go the lake, the hikers must go down the rocky caldera side through the paths, which usually used by the miners. Wet handkerchiefs are important in this area. It covers our nose from the clouds blown by the wind to the paths. Besides going to the lake, the hikers can go around the caldera for the whole day. The hiking to Ijen占쏙옙 crater is usually suggested to be done in the morning and ended at 14.00 noon, it is caused by the possibility of the changing of the wind direction to go the paths