Diego Rivera painted this series of murals, Fuente de Tláloc, for the inauguration of the Chapultepec water works (near Lago Menor). These were built in the 1940s to channel the waters of the Río Lerma, 62km west, into cisterns to supply the city. Experimenting with waterproof paints, Rivera covered the collection tank, sluice gates and part of the pipeline with images of amphibious beings and workers involved in the project. Though technically only open Saturdays, the guard can sometimes be persuaded to let you in, for a tip.