I've been to Constitution Hall and you're right the museum is wonderful. I love their library also. One of these days I want to go to the National Archives and the Library of Congress.
We enjoyed the lobby of the National Geographic building. They have photographic exhibits that were exceptional (and free).
Ford's Theatre and the Boarding House across the street are very interesting too.
The Sculpture Garden was lovely to walk through.
The WWII and FDR memorials were well done.
I didn't read above, if these are repeated, my apology.
