From Philadelphia, it's just a short 2 and a half hour drive to Washington, DC (again, see the
map view for driving directions). Once there, your first stop is the Capitol building. Free guided tours are available Monday through Saturday. In the afternoon, you should stop by a trio of sights that are very convenient to your hotel, starting with the National Archives, where the original Declaration of Independence is on display (along with other important documents like the U.S. Constitution).
Next up are the Lincoln and Jefferson Memorials: two beautiful monuments commemorating two of America's most influential presidents.