The source of the Cega river Nature · Navafría, Comunidad de Villa y Tierra de Pedraza, Segovia Image of Navafría, not of the place itself. The Cega rises on the northern slope of the sierra de Guadarrama, near the Lozoya pass, on the watershed between the Duero and Tajo basins. Its source lies in the spring known as the fuente del Mojón, in the municipality of Navafría, beneath the Peña del Cuervo, which rises above 2,100 metres and is the highest point in the municipality. Over 149 kilometres, the river crosses the provinces of Segovia and Valladolid before flowing into the Duero, and after rising it irrigates the whole of the Tierra de Pinares. In the village itself, its waters have always been used for drinking and for irrigating orchards and meadows, and they once drove old mills and forge hammers (martinetes), one of which is preserved as an anthropological museum. Photo: Javier Casado Tirado (CC BY-SA 3.0) What to see and do in Navafría