The Dieng Plateau is a volcanic highland at about 2,000 meters elevation on the border of Banjarnegara and Wonosobo regencies in Central Java. It formed as the collapsed floor of an ancient volcano and remains geothermally active, with steaming craters, boiling mud pools, mineral lakes, and a working geothermal power field.
Human history on the plateau stretches back at least to the 7th century, when Hindu communities built stone temples dedicated to Shiva — among the oldest on Java. Today the area is known for those temple clusters, for the ruwatan dreadlock-cutting ritual, for its potato farms, and for the rare dry-season frost locals call 'bun upas.'