Head to the National Zoo and say good morning to the pandas. If the weather is bad, you can still enjoy the numerous indoor animal houses. Then hop on the Metro to Dupont Circle for lunch. Walk west on tree-lined P Street NW to Georgetown, where you can shop, admire the architecture, and people-watch.
If you got a good dose of Georgetown on your first day, consider instead visiting the International Spy Museum, a Chinatown attraction that tends to be less crowded after 2 pm. From there you can easily walk to the Smithsonian American Art Museum and National Portrait Gallery, which stay open until 7.