If you venture over the Atlas Mountains from Marrakech or Fez you will eventually reach the border of the Sahara. The Merzouga Dunes, known as Erg Chebbi, about 20 miles from Erfoud, is a spectacular area within easy reach of comfortable, air-conditioned hotels. Here you can get a sense of the great vastness of this desert and, with patience and good fortune, glimpse at least a few of the unique reptiles, birds and mammals that live here. To delve deeper, you can go by camel and stay overnight in a Bedouin tent.