Canyon of the Aulencia River Nature · Colmenarejo, Cuenca del Guadarrama, Madrid The Aulencia's narrow gorge between holm oak woods and grazing pastures dotted with junipers, ash trees and Portuguese oaks, within the Regional Park of the middle course of the River Guadarrama; the path that follows it passes the old El Pilar mine. Photo: Axel Schlaefer (CC BY-SA 3.0) What to see and do in Colmenarejo