Guadarrama high-speed rail tunnel

The Guadarrama Tunnel is a railway tunnel across the Sierra de Guadarrama, forming a key portion of the Madrid–Asturias high-speed rail line in Spain. It is the largest tunnel in Spain, as well as being the fifth largest in the world at the time of its completion. The tunnel comprises two individual parallel tubes, with regular interconnecting galleries throughout their length. The western tube is 28,407 m long and the eastern tube 28,418 m long, and it is the longest tunnel in Spain (when not counting the Line 12 tunnel in the Madrid Metro). The tunnel was opened for traffic in December 2007, and has been primarily used by the AVE high speed passenger trains.

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).