Located in the western end of Vizcaya, on the border with Cantabria, Armañón or Ranero natural reserve forms a relevant mountainous massif in the landscape of Las Encartaciones. It extends among the valleys of the Carranza and Agüera rivers, in a succession of hilly and mountainous lands of eminently rural character which occupy a surface area of 2,996 hectares. Armañón peak (854 m) constitutes the highest summit of the massif, although also notable are other mountains such as Ranero (737 m), Surbias (638 m) and Los Jorrios (837 m).
The landscape is mainly calcareous with spectacular reliefs, in which it is frequent to come across karstic forms, with ridges, grikes, dolines, fissures... The subsoil is lined with over 200 catalogued caves and abysses which have great geological, palaeontological, spelean and biological value. Pozalagua Cave is a must-see in this natural space. Discovered in 1957, it is notable for the singular eccentric stalactites which, instead of forming downwards, ramify in any direction. The cave is 2 km from the Ranero district in the municipality of Valle de Carranza, and is suitably equipped to receive tourist visits. We should also mention the Torca del Carlista, one of the largest cavities in Europe, which is over 400 metres long, 250 metres wide and 90 metres high.