Peña Rubia Nature · Guadalix de la Sierra, Cuenca Alta del Manzanares, Madrid Image of Guadalix de la Sierra, not of the place itself. A limestone cliff looking out over the Pedrezuela reservoir, a rarity in a comarca of granite, riddled with caves and rock shelters. Its climbing routes stay closed from 1 January to 31 July so as not to disturb the birds breeding on its walls. Photo: Garcellor (CC BY-SA 4.0) What to see and do in Guadalix de la Sierra