Piedras Rojas is the far point of the long southern day trip, about 150 kilometres from San Pedro beyond Socaire and the altiplanic lagoons. The setting is the Salar de Aguas Calientes: a white salt crust, a turquoise lake, and a field of boulders stained deep rust-red by oxidised iron, all of it at just over 4,000 metres with Láscar smoking away to the north.
It is the most photographed landscape in the region after the Valle de la Luna, and unlike most of those photographs it does actually look like that. The colour is not enhanced; it is iron. Laguna Talar sits immediately alongside, so the two are visited together.
Two practical things. The access is controlled by the Socaire community and has been closed to visitors for extended periods in the past — check before you book a tour that promises it. And it is a very long day: eleven or twelve hours, most of it above 3,500 metres, usually combined with Miscanti and Miñiques. Eat before you go and do not attempt it on your first day in town.