The Tren a las Nubes (Train to the Clouds) is a tourist train service in Salta Province, Argentina.
The service runs along the eastern part of the Salta–Antofagasta railway line of the Belgrano Railway (also known as the “C-14” line) that connects the Argentine Northwest with the Chilean border in the Andes mountain range, over 4,220 metres (13,850 ft) above mean sea level, the fifth highest railway in the world.
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 for traction, the route had to be designed to avoid steep grades. The zigzags allow the train to climb up driving back and forth parallel to the slope of the mountain.
It departs from Salta every Saturday at 07:05, and returns around midnight, though most tourists simply do the 8-hour one-way trip and return by other means. The train is composed of a dining carriage, bar carriage, a first aid area and two passenger carriages with room for 170 people, though this is expected to increase to 400 over time.