El Pas de la Casa in the context of "Envalira Tunnel"

The Ariège (French pronunciation: [aʁjɛʒ] ; Occitan: Arièja; Catalan: Arieja) is a river in southern France and Andorra. It is a right tributary of the Garonne. From its source in the Pyrenees near El Pas de la Casa, the river flows north, forming part of the French border with Andorra. It flows for about 163 km (101 mi) and drains approximately 4,200 km (1,600 sq mi) of mainly mountainous terrain. The river is managed by the authority of the Agence de l’eau Adour-Garonne, to preserve the water quality, ensure ecological continuity, and regulate hydropower use.

Port d'Envalira (el. 2408 m.) is a mountain pass in the Pyrenees in Andorra, that connects El Pas de la Casa with the rest of the country. It is the highest paved road in the Pyrenees. The climb has been featured several times at the Tour de France and Vuelta a España cycling races.

The construction of a toll tunnel to avoid the mountain pass started in 1999 and opened to traffic in 2002. The tunnel is located at an altitude of about 2000 metres and is nearly 3 kilometres long.