Royal Glass Factory Monument · Real Sitio de San Ildefonso, Alfoz de Segovia, Segovia It was born in 1727 when the master glassmakers Buenaventura Sit and Carlos Sac set up a furnace paid for by the crown to supply the palace with glass and mirrors. The present Neoclassical building, of granite masonry, was raised between 1770 and 1784 after a fire. Photo: Zarateman (CC0) What to see and do in Real Sitio de San Ildefonso