Built between 1799 and 1805, Dumbarton House is the headquarters for the National Society of Colonial Dames of America. Stop here to admire gorgeous architecture and antique decorative arts, and to glean a bit of early American history. Self-guide your way through the house, whose collection contains more than 1,000 paintings, ceramics, and furniture from the Federal period. You can reserve timed tickets in advance, but walk-up visits are also welcome.