The headquarters of the American diplomatic corps is a forbidding, well-guarded edifice – modernist, monolithic and unfriendly. In stark contrast are the elegant, grand diplomatic reception rooms, where Cabinet members and the Secretary of State entertain visiting potentates amid ornate 18th-century American art and antiques. Tours of the rooms are by reservation only; telephone or go to the website at least 90 days beforehand to request a spot. Bring photo ID to the tour.