This museum is close to Dulles airport and our wedding venue. It is the much larger location of the Smithsonian Air and Space Museum. It has over 200 aircraft, gliders, and spacecraft. Admission is free but parking is $15. There are not many food options near the museum but there is a Shake Shack inside.
This is the mall near our venue in case you forgot something. It is also near Tysons Galleria which is the "fancy" mall with designer stores. Though the two locations are walkable, the area is designed for cars and not very pedestrian friendly.
If you are in the mood for even more gardens, this is the national botanic garden with a large two-story conservatory. Taking the silver line train to the Federal Center SW station will require an 11 minute walk, but avoids the stress of driving and parking in downtown DC. This garden is across the street from the Museum of the American Indian where we plan to have lunch on Saturday.