A free exhibition that’s unfairly overlooked is The Library of Congress. Created by an act of Congress in 1800, this often-overlooked Washington landmark occupies a resplendent 1897 building connected by tunnel to the Capitol building. A bibliophile's dream, the Library of Congress hosts a staggering 144 million items on 532 miles of shelving, all organized beneath a gold-bedecked ceiling. (The mosaics, sculptures, and paintings of the Great Hall and Main Reading Room are themselves worth a trip down.) First drafts of the Declaration of Independence, Lincoln's Gettysburg Address, and a Guttenberg Bible are all in residence, along with other historical treasures and 33 million books.
Insider Tip: Classical music concerts are offered free throughout the year at the Library of Congress concert hall located below ground.