It looks like a palace—because it was. Started in the 18th century as a private collection of Empress Catherine II, it contains artwork collected by the Russian czars. It became public museum in 19th century. Its six buildings hold more than 3 million items from Russia, including amazing jeweled Easter eggs created by Carl Faberge.

Top Art: Madonna with a Flower (Leonardo da Vinci), St. Sebastian (Titian), Dance (Henri Matisse), Woman with a Fruit (Paul Gauguin).

New York City—Containing the greatest collection of art in the U.S., it was founded in 1870. In addition to American and European paintings, it displays medieval art and armor, masks from Africa, mummies from Egypt, Aztec gold sculpture, as well as treasures from Asia, the Middle East and ancient Greece and Rome.

Top Art: Death of Socrates (Jean-Jacques David) Self Portrait (Rembrandt), Cypresses (Vincent van Gogh), Midnight Ride of Paul Revere (Grant Wood), The Harvesters (Peter Brueghel the elder), Young Woman with a Water Jug (Jan Vermeer).

Once one of the world's largest palaces, it is now one of the world's largest art museums-and maybe the most famous one. Since 1793 it has been gathering an incredible collection of ancient and Western art, including 6,000 European paintings dating from the 13th century to the middle of the 19th century. It would take many hours to walk through all its vast halls.

Top Art: Mona Lisa (Leonardo da Vinci), Venus of Milo, Victory of Samothrace, Slaves (Michelangelo), Embarkation for Cythera (Antoine Watteau) Wedding at Cana (Veronese), The Lacemaker (Jan Vermeer), The Raft of the Medusa (Theodore Gericault)

Finished in 1819, the Prado was originally a museum of natural history, but the royal family decided to use it to hold its paintings. In 1868, it became a national museum. It is famous for its collection of Spanish, Flemish and Venetian paintings. The Prado owns more than 10,000 artworks, but only 2,000 are displayed at any one time.

Top art: Naked Maja (Goya), Burial of the Count of Orgaz (El Greco), Maids of Honor (Diego Velazquez), Adam and Eve (Albert Durer), Garden of Earthly Delights (Hieronymus Bosch)

This palace holding the museum was built in the 16th century for Cosimo I de' Medici. In 1591, the public was allowed to view the artworks inside, making the Uffizi the first public art museum in the world. Today, the Uffizi's 45 rooms hold 1,700 paintings, 300 sculptures and 45 tapestries. Among its wonders is the world's best collection of Renaissance art.

Top Art: Primavera and Birth of Venus (Sandro Botticelli), Annunciation (Leonardo da Vinci), Holy Family (Michelangelo), Judith and Holofernes (Judith Gentileschi), Venus of Urbino (Titian)