The Atacama's altitude and the San Pedro base

San Pedro de Atacama sits at 2,400 meters, and many of the excursions (the Tatio geysers at dawn, the altiplano lagoons) climb above 4,000; take the lower ones first and drink water constantly. The desert's night sky is the clearest on Earth; an astronomy tour on a moonless night is the thing to book. Tours are sold by dozens of agencies on the main street at similar prices; the difference is group size. Sunscreen and a hat are essential; the UV is extreme.