The Smithsonian
Many people who aren’t local don’t realize that the Smithsonian isn’t actually one museum, but dozens. Most of the great museums in DC are part of the Smithsonian, and most are free. I repeat: MOST ARE FREE! Take advantage of this, because they are some of the greatest museums in the world, and your jaw will be on the floor the entire time. Like the Mall, I considered listing out each museum in the Smithsonian as its own entry, but there are just too many. My must-see free museums are the Air & Space Museum, American Art Museum, American History Museum, and National Portrait Gallery. I also highly, highly, highly recommend the Renwick Gallery, Cooper Hewitt, and the Hirshhorn—you have to pay to see these, but they are completely worth it.