Upcoming Historical Tourism Adventure

In September my partner is attending a work conference just outside of Washington, DC.  I've decided I'm going to tag along on the trip and explore some of historic sites, museums, and general history goodness in the area. So far I've come up with a few must see places, but I would love to hear suggestions from anyone who is familiar with the area and who has a general love of history.

The must see list so far:

• American Indian Museum.  Given the lack of national Indigenous museum in Canada I'm intrigued to see how the American Indian Museum portrays the complex First Nation-Settler history.  My visit to the CMC's First Peoples Hall a couple of years ago was disappointing at best.  
• National Museum of American History.  The desire to make this visit is mostly based on the insistence recommendations of colleagues and friends.
• National Archives and Records Administration.  The desire to visit the National Archives is once again based in the desire to compare national differences.  Library and Archives Canada is far from welcoming to the casual visitor and has very little in terms of exhibits and public vaults. 

If time permits I would also like to make a visit to one of the numerous art galleries or art museums.  If you have visited Washington in the past what were some of your favourite experiences?