With a collection of more than 150,000 works, including paintings, prints, sculptures and photographs, the National Gallery of Art in Washington traces the history of western art from the Middle Ages to the present day. The most-visited art museum in America, it’s home to the only painting by Leonardo da Vinci in the Americas (a portrait of Ginevra de’ Benci) along with masterpieces by Titian, Raphael, Vermeer, Rembrandt, Monet, Matisse, Degas (pictured) and many other European greats. But the American collection is equally strong, including work by Mary Cassatt, Thomas Eakins, John Singer Sargent and Edward Hopper. Also, it's free.