The vast area covered by the Arab World encompasses wide and diverse geographical features ranging from deserts and shrublands to Mediterranean forests and snow-capped mountain ranges. Deserts reign in most of northern Africa where the Sahara exists, the world's hottest desert where some of the sand dunes can reach 180 metres (590 ft) in height. The Arabian Peninsula is mainly covered by a range of deserts: the Nefud in the north, which is a stony desert; the Rub' Al-Khali or "Great Arabian Desert" in the south, and between them, the Dahna desert.