Top choice notable building in Arlington

South of Arlington Cemetery is the Pentagon, the largest office building in the world and the headquarters of the US Department of Defense, the Army, Navy and Air Force. Outside the building is the Pentagon Memorial; 184 illuminated benches honor each person killed in the September 11, 2001, terrorist attack on the Pentagon. To get inside the building, you'll have to book a free guided one-hour tour on the website and provide appropriate photo ID. Make reservations 14 to 90 days in advance.