The Pico de Tres Mares (Three Seas) got its name because it is the source of three main rivers which flow from it into three different seas - the Híjar, tributary of the Ebro which flows into the Mediterranean, the Pisuerga, tributary of the Douro which flows into the Atlantic and the Nansa which flows into the Cantabrian sea. This peak, which rises to 2 175m, reveals a splendid circular panorama to the north of the Nansa, to the east of the Sierra de Peña Labra and the Montes de León, and to the west of los Picos de Europa.