Between the Gilf Kebir and Siwa Oasis lies the awesome immensity of dune fields that the explorer Gerhard Rohlfs named the Great Sand Sea (Bahr er-Raml in Arabic). Covering 72,000 square kilometres (roughly the size of Ireland), the Sand Sea extends for an average of 650km from north to south and 300km from east to west. Roughly two thirds of this consists of parallel seif dunes, sometimes over 100m high and as much as 150km long, separated by flat “corridors” one or two kilometres wide, whose northwest–southeast alignment is determined by the prevailing wind.

While these seif dunes are ever-moving, satellite imaging has shown that they sit atop stable whalebacked dunes. Elsewhere in the Sand Sea, where seif dunes have descended escarpments, they have reformed as crescent-shaped barchans. Though shifting sands seem the only “life” in the Sand Sea, a little vegetation exists, lying dormant for years until a brief shower of rain revives it.

This spectacularly alien terrain has long fascinated explorers and scientists; now tourists are venturing in to marvel at its wonders. A brief excursion from Siwa Oasis to Bir Wahed will let you experience its colossal dunes without spending a fortune, while the following sites can be visited on deep-desert safaris.