Philadelphia Museum of Art

Most people meet this museum from the bottom of its steps, running up all 72 of them with their arms over their heads, because that is what Rocky Balboa did in the 1976 film and visitors have copied him ever since. A bronze Rocky stands beside the stairs to prove it. What they are running toward is a building shaped like a Greek temple, opened in 1928 on a rise at the end of the Benjamin Franklin Parkway, its pediments picked out in blue, red and gold the way an ancient one would have been.

Inside, past the armor and the transplanted period rooms, is one of the reasons art historians come: the largest collection of Marcel Duchamp anywhere. Walter and Louise Arensberg, collectors who knew Duchamp personally, left the museum their holdings around 1950, and with them came 'Nude Descending a Staircase', the figure broken into overlapping slices of motion that scandalized New York in 1913.

In a small room off to the side sits his last work, 'Étant donnés', which you can only see by looking through two peepholes in an old wooden door. Duchamp built it in secret over 20 years and left instructions that it be assembled only after his death, which is how it reached Philadelphia in 1969.