San Pedro is a timeless adobe town with a laid back atmosphere and an erratic electricity supply. Its dusty streets are lined with bars, cafés and tour operators offering various kinds of excursions into the surrounding desert. The excellent museum here has a comprehensive history of the indigenous population and an interesting display of local archaeological discoveries.
Should you choose to take the morning optional excursion to El Tatio Geysers, be prepared for a very early start. But it's well worth it. You arrive on the pitted, craggy geyser field just before dawn, and as the sun rises and warms the earth, hot steam projects dramatically out of the crater into the freezing morning air, creating a wall of mist through which you can make out dark silhouettes and the penetrating sunlight. Note that a rapid ascent to an altitude of 4,500m makes this excursion unsuitable for some.
Alternatively you may want to walk to Pukará de Quitor (3 km). This old Inca fortress has superb views of the mountains and volcanoes bordering Bolivia and Argentina.
On the included excursion to the Moon Valley you arrive late afternoon to explore shady gorges and dramatic canyons formed over centuries by the erosion of salt mountains. Just before dusk, climb to the ridge of a vast golden sand dune to see the landscape lit up in different shades of pink, crimson and mandarin cast by the setting sun.