Trail of los Molinos de Colmenar del Arroyo Activity · Colmenar del Arroyo, Sierra Oeste, Madrid Image of Colmenar del Arroyo, not of the place itself. A path of some 3.5 kilometres linking the municipality's water heritage: the mill races, the washing place, the drinking trough, the waterwheel and the Caño bridge, a record of the part water played in the village's rural economy. Photo: PePeEfe (CC BY-SA 4.0) What to see and do in Colmenar del Arroyo