Mexico City is home to many historic sites, including the Castillo de Chapultepec, the only castle built in North America. It has the most museums of any city and many theaters. Important buildings include the Cathedral, Palacio Nacional, and Angel of Independence. The city was built on an ancient lake and volcanoes like Popocatepetl can be seen from the city. It has hosted the World Cup twice and the Olympics, and sites like the Estadio Azteca and Ciudad Universitaria are of cultural significance.