The Guadarrama as it passes through Serranillos del Valle Nature · Serranillos del Valle, Comarca Sur, Madrid Image of Serranillos del Valle, not of the place itself. The municipal district falls within the Regional Park of the middle course of the River Guadarrama and its surroundings, created by Law 20/1999: a strip of some fifty kilometres and more than twenty-two thousand hectares following the river from north to south. Photo: Dirección General de Turismo. Consejería de Economía e Innovación Tecnológica. Comunidad de Madrid. (CC BY 3.0 es) What to see and do in Serranillos del Valle