Tren a las Nubes - Train to the Clouds (Argentina)

The Tren a las Nubes (Train to/of the Clouds) is a touristic train service in Salta Province, Argentina.

The service runs along the eastern part of the C-14 line of the Ferrocarril General Manuel Belgrano, connecting the Argentine Northwest with the Chilean border in the Andes mountain range.

At over 4,220 meters (13,850 ft) above mean sea level, it's the third highest railway in the world. Originally built for economic and social reasons, it is now primarily a tourist attraction as a heritage railway.

The railway line has 29 bridges, 21 tunnels, 13 viaducts, 2 spirals, and 2 zigzags. Because of the design decision not to use a rack-and-pinion system for traction, the route had to be designed to avoid steep grades.

The zigzags allow the train to climb, travelling back and forth parallel to the slope of the mountain. (Link)