The Smithsonian is the world’s largest museum complex, with 21 museums and the National Zoo. Eleven museums are located along the National Mall in Washington, D.C., six others and the Smithsonian’s National Zoo are nearby. All of these museums are free, so even if you have just an hour its worth it to pop in and see the beautiful architecture. **The below museums are free but do require you to reserve a free pass in advance (we'd recommend booking a few weeks before you plan to go): African American History and Culture Museum Air and Space Museum in D.C. National Zoo