The Colosseum (Underground), Italy
Rome's Colosseum, an ancient amphitheater and former gladiator battleground, is one of the world's most famous attractions. But most people don't know that there's a whole secret section that can now be explored—the underground. In 2010 the Italian government decided to allow small groups of visitors inside the Colosseum's subterranean level to see where gladiators made their grand entrances from and their final exits (at the Porta Libitina, the arch through which bodies were removed). Visitors can also see where exotic animals like lions and tigers were held below ground before being hauled up in elevators to appear suddenly before the screaming crowds.