Ijen plateau or known as "Kawah Ijen" is highly recommended to mountain buffs and hikers. The Plateau was at one time a huge active crater, 134 sq km in area. At the rim itself you have a nice view on the lake. The walk up to the crater rim takes 60-90 minutes. It's pretty steep. The magnificent turquoise sulfur lake of Kawah Ijen lies at 2148 m above sea level and is surrounded by the volcanos sheer crater walls. The vent is a source of sulfur and collectors work here, making the trek up to the crater and down to the lake every day.