Chapultepec Park houses the Chapultepec Castle, now a museum on a hill that overlooks the park and its numerous museums, monuments and the national zoo and the National Museum of Anthropology (which houses the Aztec Calendar Stone). Another piece of architecture is the Palacio de Bellas Artes, a white marble theater/museum whose weight is such that it has gradually been sinking into the soft ground below. Its construction began during the presidency of Porfirio Díaz and ended in 1934, after being interrupted by the Mexican Revolution in the 1920s. The Plaza de las Tres Culturas, in this square are located the College of Santa Cruz de Tlatelolco, that is the first and oldest European school of higher learning in the Americas, and the archeological site of the city-state of Tlatelolco, and the shrine and Basilica of Our Lady of Guadalupe are also important sites. There is a double-decker bus, known as the "Turibus", that circles most of these sites, and has timed audio describing the sites in multiple languages as they are passed.