Spread out across the Arabian Peninsula lies the large desert country of Saudi Arabia, a distinctly hot and dry place year round. Starting from the west is the only relatively humid place, the western coastal region of Tihama bordering on the Red Sea. Parallel to the Red Sea coast run the country's major mountain ranges, the Hejaz range in the northwest and Asir range in the southwest. The mountains of Asir rise up over 3000 m, and are a green and cool refuge for Saudi Arabians who want to escape from the summer heat. Behind these mountains towards the east, north and south are wide expanses of a high (semi-)desert plateau called Nejd (or Najd), gradually sloping down toward the Persian Gulf in the east and to the true desert of Rub'al Khali or Empty Quarter in the south. Apart from several large and modern urbanized oases, the inland areas are largely unpopulated. A few minor mountain ranges are found here, such as the Tuwaiq escarpment near Riyadh, and the northern highlands of Shammar.
Given the extremes of Saudi desert and climate, it is not surprising that hiking does not appear to be a popular local passtime. There are no long distance hiking trails whatsoever, and the adventurous usually set out by 4WD and do short hikes of a day or a few hours. Yet there are some wonderful landscapes waiting to be explored, particularly in the western mountains of Hejaz and Asir. Rugged massifs and wadi's (valleys), very old donkey and camel trails that have fallen into disuse, and magnificent volcanic craters like Al-Wahbah, Jabal Bayda and Jabal Abyad.
There appear to be few provisions for hikers, so if you want to camp anywhere, bring all you need. Keep in mind that temperatures higher up can drop real low at night, and winds can be strong too.