San Pedro de Atacama is built around tours, but not every sight needs one. Altitude and distance are what decide it.
Worth a tour
High-altitude lagoons and the geysers at sunrise: the roads are long, the start is very early and a driver who knows the altitude is worth paying for.
Do it yourself
Valleys close to town are easy by hired bike. Carry more water than you think and turn back before the afternoon heat.
