The Highlands of Iceland are mostly uninhabitable and cover most of the interior of the island. Its roads are only open during the summer, (June-August) and then only accessible by 4WD vehicles. The highlands contain grand mountains, expansive lava fields, black sands and most of Iceland´s glaciers. The best known highland roads are Kaldidalur, Kjölur and Sprengisandur. Most of the roads are made of loose gravel, and many rivers are not bridged, making the driving difficult and challenging. Off-road driving is forbidden in the Highlands.

http://www.visiticeland.com/DiscoverIceland/Regions/TheCentralHighlands/