Washington D.C. is the capital of the United States, where many political and historical events have taken place. The document discusses several important landmarks and monuments in D.C., such as the Washington Monument, Lincoln Memorial, and Vietnam Veterans Memorial. It also mentions significant buildings like the White House and Capitol Building, as well as influential historical figures to the city, including George Washington, Abraham Lincoln, and James Smithson. The Smithsonian Institution's museums are highlighted for preserving U.S. history and making unique artifacts available for public viewing.