National Air and Space Museum

The world's most-visited museum is heavenly for adults and a must for kids. A seemingly endless assemblage of artifacts from the history of flight—from the Wright brothers 1903 flyer to the Apollo 11 space module—are exhibited here; interactive experiences run the gamut from climbing in rockets and touching moon rocks to IMAX films and heart-stopping rides in flight simulators.

Tip: While the National Museum of American History is under renovation (until summer 2008), you'll find such national treasures as Lincoln's top hat, Jefferson's Bible, and Dorothy's ruby slippers on display here, too.

Admission: Free.