Glass furnaces of Cadalso Curiosity · Cadalso de los Vidrios, Sierra Oeste, Madrid Image of Cadalso de los Vidrios, not of the place itself. The town's second name comes from its glass kilns, which in the 16th and 17th centuries supplied much of the glassware of the Royal Apothecary of the monastery of El Escorial; production continued until the early 20th century, when it closed for good. Photo: Dirección General de Turismo. Consejería de Economía e Innovación Tecnológica. Comunidad de Madrid. (CC BY 3.0 es) What to see and do in Cadalso de los Vidrios