The Tren e las Nubes or Tren a las Nubes (Train of/to the Clouds) is a train service in Salta Province of Argentina, that connects the Argentine Northwest with the border with Chile in the Andes mountain range, over 4,220 metres (13,850 ft) metres above mean sea level, the third highest railway in the world. Originally built for economic and social reasons, it is now of primarily touristic value as a heritage railway.