Last month (my birthday to be precise) Phil and I flew out to D.C. without the kids. We had a great time and our "office" window was awesome. We took up the tourist name for a day and even did the metro. We saw the monuments, White House, Capital, the Smithsonian museums etc., but mostly enjoyed our time with our good friends who let us invade their home and stay with them for the week. On a side note, did you know that Night at the Museum wasn't not even filmed in the actual museum? It was filmed partly in the Air and Space museum, but the majority of the museum was filmed in Canada. Those pictures will be posted at a later date.
Great Falls National Park is a place I highly recommend if you are in the area. It's beautiful. The couple that flew us out there for their engagement pictures were so cute.