Make sure you bring cash to Washington, D.C. Not that it’s expensive (actually, many museums are free) or that no one accepts plastic (they do)—it’s just an awful lot of fun to hold up a $5 bill next to the actual Lincoln Memorial, or a $20 in front of the White House. In between touring monuments and historical sights, check out the quirky International Spy Museum, watch pandas at the National Zoo, or catch a military band playing an outdoor concert on Capitol Hill.