The Foz de Lumbier is carved out of the limestone rock by the river Irati at the western end of the Leyre range of mountains, at the foot of the Navarrese Pyrenees. It is one of the most spectacular gorges in Navarre, a landscape created over millions of years by the waters of the river Irati, which have left their mark on this sanctuary of nature day by day. The gorge was declared a Nature Reserve in 1987. Lumbier is a narrow and small gorge, just 1,300 metres long, but of spectacular beauty. Its vertical walls reach a maximum height of 150 metres and large birds of prey live in the cracks and ledges, with species such as griffon vultures and lammergeirs (bearded vultures). It is also a refuge for foxes, boar, badgers and owls, and is strewn with gall and kermes oaks and bushes such as thyme, lavender and gorse that hang from the cracks of the limestone cliffs. The vegetation that is transformed into woods of poplars, willows and ash trees at the entry and exit of the gorge.