The National Mall + Smithsonian museums (free entry, tons to see)  Monuments & memorials (Lincoln, WWII, Vietnam, etc.) 
Stunning natural park with waterfalls and scenic overlooks!
Coblestones streets, waterfront views, and classic row houses. Visitors love strolling along M Street for shopping and dining, exploring the scenic waterfront at Washington Harbour, or walking through the beautiful campus of Georgetown University