Royal Irrigation Canal of the Jarama Monument · San Martín de la Vega, Las Vegas, Madrid Image of San Martín de la Vega, not of the place itself. An irrigation canal designed in the 16th century and begun under Felipe II, which takes water at the Presa del Rey and carries it to the Tagus; its sluice houses and aqueducts punctuate the floodplain and the works were not considered finished until 1968. Photo: LBM1948 (CC BY-SA 4.0) What to see and do in San Martín de la Vega