Generally, every federal museum, monument and memorial is open year round, except Christmas Day, New Years Day and possibly some other public holidays.
The Smithsonian Institution has about ten museums, including the Air and Space Museum, the Museum of American History and the Natural History Museum. None of these make any charge for entrance.
Other places said to be worth considering visiting include the White House, the FBI building, the Capitol, the Washington Monument and the Lincoln Memorial.
Southeast and southwest DC are reported as being best avoided for personal security reasons.
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Places & useful connections
Before you set out
Confirm current access, opening arrangements, reservations and the suitability of your planned roads and walks. Photographs may show earlier conditions.