If you’re going to make one weighty and educational stop in D.C., the Library of Congress should be it. Less well known than many of the Smithsonian sites, this massive complex contains way more than just research books, featuring more than 130 million items on permanent exhibit. Spread out over three architecturally splendid buildings, the Library of Congress houses a wide array of exhibitions, covering topics from Christopher Columbus to the Founding Fathers to the history of television. If you really want to see the library, you’ll need a full day to visit the gigantic collection. If you have limited time, you’ll want to check out Thomas Jefferson’s library and the American Treasures exhibit, two massive colonial halls that instantly take you back to Revolutionary times. This one is probably a little too heavy for the kids, and consequentially, far less crowded than most of the National Mall.