The Monks of the Pacana are a group of pale rock columns standing in the open at about 4,500 metres, on the long track out to the Salar de Tara. The tallest is around twenty metres. They are what is left of an ignimbrite sheet — welded volcanic ash from an enormous eruption — after two million years of wind has taken away everything softer around them.
They look deliberate, which is the whole effect: a handful of figures on an empty plain with nothing else in any direction. The name is obvious once you see them. There are more columns scattered for several kilometres around, and the ground between them is strewn with pumice light enough to float.
Getting there means the full-day Tara excursion, a rough four-hour drive each way from San Pedro on unpaved track, at altitudes that stay above 4,000 metres for most of the day. It is the most demanding of the standard trips and the one people most often say was worth it.