The Ferrocarril del Sur climbs to some of the highest elevations of any train line on earth, cutting through the Peruvian Andes on a route long considered a feat of railway engineering. The film rides the Andes Explorer from Cusco, the old Inca capital, across high passes toward Puno on the shores of Lake Titicaca and on to the white volcanic-stone city of Arequipa, with a branch line leading to the ruins of Machu Picchu. Cameras follow the train through switchbacks and thin mountain air, past terraced farmland, indigenous villages, and stretches of landscape with no roads at all, while the crew and passengers describe what keeps a century-old line running at these altitudes. The documentary treats the railway as both an engineering story and a way into a region most travelers never reach overland, showing the maintenance work, the weather, and the isolation that make this stretch of track as demanding to keep operating as it was to build.