Kawah Ijen - World's largest highly acidic lake

On the west of Gunung Merapi (The Mountain of Fire), is the 1km wide turquoise colored acid crater lake called Kawah Ijen (World's largest highly acidic lake). It is inside a larger caldera of The Ijen Volcanoes. In this photo, the shadow falling on the lake is that of the Gunung Merapi itself.

The Gunung Merapi is the highest peak of the Ijen Volcanoes that lies at 2,930 m (9,613 ft) and the Kawah Ijen at 2,799 m (9,183 ft) above sea level.