Crescent-shaped sand dunes rise and fall steeply, some up to a 100 metres high. The sun beats down from the sky and it is exhausting to walk. Your boots sink deep into the northern Chilean golden sand. But it is worth it, when you reach the ridges of the sand mountains near Copiapó and are rewarded with the sight of a dune landscape that never seems to end. South America’s answer to the Sahara, the southern part of the Atacama Desert is known as the “Mar de Dunas” with a “sea of dunes” that spans 335 square kilometres. At 550 metres, El Medanoso is one of the highest dunes on the continent and…