Excavated on limestone rock of the Leyre range, the mouth of Lumbier and the mouth of Arbayún are two of the most interesting natural spaces of Navarre, declared by the Government of Spain Natural Reserve in 1987.
The mouth of Lumbier is a narrow canyon of a kilometer of length excavated by the waters of the Irati river; It runs between steep walls of heights between 150 and 200 meters high. This narrow space of the mouth of Lumbier counts on a conditioned road that follows the old route of the Train of Irati (the first electric railway of Spain) that covered the line between the historical and beautiful towns of Pamplona and Sangüesa. The route through the Lumbier estuary includes two tunnels excavated in the rock, which lack artificial lighting. Another of the characteristic features of the mouth of Lumbier are the ruins of the Bridge of the Devil; It was flown by the French troops in 1812 during the campaign against the patriotic guerrilla in the War of the Independence; According to a legend is associated with pacts with dark forces.
Just 17 kilometers from the mouth of Lumbier is the mouth of Arbayún, which with its 6 kilometers in length is the longest in Navarre. The Salazares river is responsible for its erosion and the main axis of this space that marks one of the entry points to the Navarrese Pyrenees.
Between the mouth of Lumbier and the mouth of Arbayún are the Acantilados de la Piedra and San Adrián, another environment declared Natural Reserve full of natural arches and other interesting karst formations. Both the mouth of Lumbier and that of Arbayún and the cliffs of the stone present a vegetation composed largely of forest masses of poplar, oak, pine, ash and cinder along with other shrub-like populations. As for its fauna, it is possible to emphasize that the mouth of Lumbier and the one of Arbayún contain the greater colony of griffon vulture of Navarre. There are viewpoints from which you can observe these animals accompanied by other birds such as the eagle, the vulture or the bearded vulture.
The mouth of Lumbier can be easily traversed by foot through the Greenway that crosses it. It also has a large parking at the entrance. The mouth of Arbayún is not equipped for its route following the river bed, but it can be observed its profile from some points like the viewpoint of Iso, located in a projection on the river.
The population of Lumbier (see specialized page) is the center of all this natural set. The access to the mouth of Lumbier is clearly signposted from it and to reach the mouth of Arbayún it is convenient to take the road NA-178. The access to Lumbier is made through the road NA-150, that leaves of the A-21, between Pamplona and Jaca.