Aqueduct of la Retuerta Monument · San Agustín del Guadalix, Cuenca del Medio Jarama, Madrid Image of San Agustín del Guadalix, not of the place itself. At 170 metres long and 28 high, it is the most striking work among the five channels of the Canal de Isabel II that cross the municipal district. It formed part of the water supply system to Madrid inaugurated by Queen Isabella II in 1858. Photo: Zarateman (CC0) What to see and do in San Agustín del Guadalix