Library of Congress

The world’s largest library, it is housed in three different buildings and contains around 120 million items, including 22 million books, in addition to manuscripts, maps, photographs, films and prints. The first map to include the word ‘America’ and Thomas Jefferson’s personal collection are also housed here.
The visitors center in the Jefferson building shows a brief film and there are guided tours.
Capitol Hill
Tel: (202) 707 5000 (info) 

More Places-To-Visit in Washington-DC
Adams Morgan
Arlington Cemetery
Arlington House
Georgetown University
International Spy Museum
Jefferson Memorial