One of my sisters, a friend, and I spent three days in Washington, D.C. for my 30th birthday. We went to the National Museum of Natural History, the Cherry Blossom Festival parade, Sakura Matsuri Street Festival, the White House (not inside), the Washington Monument (not inside), several restaurants and shops, and a park (I'm not sure which). I also rode the Metro for the first time!
Washington, D.C. is the nation's capital of the United States of America, with 100+ FREE things to do around the area at all times of the year, including parks, museums, monuments, memorials, national historical landmarks, gardens, parades, events, and festivals. Washington, D.C. is a melting pot of the numerous cultures from around the World, and there is something for everyone.