Blue white salt desert hills in Salar de Antofalla salt flat, Catamarca, Argentina

While the Salar de Uyuni in neighboring Bolivia is the world’s largest salt flat, this Argentine natural wonder is the world’s longest. Meandering almost a hundred miles through the high Andes, the Salar de Antofalla is low on crowds and empty of luxuries like salt hotels. Arid and hard to access, the slender basin nonetheless shows evidence it once teemed with life: The flats are bounded by oncolites, stone formations made up of clustered, petrified cyanobacteria.