Acropolis of Athens

The UNESCO World Heritage Site containing the Parthenon -- the most influential building in the history of Western architecture, completed in 432 BC as a temple to Athena and still structurally intact despite being used as a church, a mosque, and a gunpowder store over 2,500 years -- receives 3.3 million visitors annually and is the most photographed monument in Europe after the Eiffel Tower. The Acropolis Museum at its base contains 4,000 objects including the original Parthenon sculptures not removed by Lord Elgin to the British Museum.