Siena''s Cathedrale di Santa Maria, or Duomo as it''s more popularly known, is a real treasure trove of Tuscan art. The 13th-century building on the site was designed by the famous Gothic architect, Pisano. A century later, work was started to make Siena''s cathedral as magnificent as St Peter''s in Rome.Today, tourists can see the walls of the uncompleted project, together with the original building and its many attractions. Visitors should look out for the distinctive exterior, the black-and-white tiled bell tower, some fine mosaics and an interesting crypt.