The Pentagon. Washington, D.C. We didn't take a tour, but we drove by. It was great to finally see it after hearing about it all my life! There was some terrorist that tried to fly some explosives into it the day we were there but, of course, they caught him in time. Crazy!
Also on these boards
National Building Museum - A beautiful and historic building located in downtown DC. Originally the Pension Building and home of the phrase "Cutting through the Red Tape".