Caldera, Iceland.
The largest crater in the Dyngjufjöl volcanic massif, Askja lies 20 mi (32 km) north of Vatnajökull, Iceland's largest ice field. Its rugged peaks, up to 4,954 ft (1,510 m), encircle a lake of 4.25 sq mi (11 sq km) that occupies the caldera. The volcano erupted in 1875 and again in 1961.