It is formed by the municipality of Candín with two slopes, Sil and Navia, and separated by the Ancares pass.

Today, Os Ancares also refers to a broader region that straddles the provinces of Lugo and León.

A range of mountains called in Galician the "Serra dos Ancares" forms the border.

Os Ancares has mountain valley high altitudes and steep slopes located in the northwest of El Bierzo.

Os Ancares Lucenses y Montes de Cervantes, Navia y Becerrea has been declared a biosphere reserve.