Officially an "international zone," not part of the United States, the U.N. Headquarters is a working symbol of global cooperation. The 18-acre riverside tract, now lushly landscaped, was bought and donated by oil magnate John D. Rockefeller Jr. in 1946. The headquarters were built in 1947-53 by an international team led by Wallace Harrison. The slim, 505-foot-tall green-glass Secretariat Building; the much smaller, domed General Assembly Building; and the Dag Hammarskjöld Library (1963) form the complex, before which fly the flags of member nations in alphabetical order, from Afghanistan to Zimbabwe, when the General Assembly is in session (mid-September to mid-December). Architecturally, the U.N. buildings are evocative of Le Corbusier (the influential French modernist was on the team of architects that designed the complex), and their windswept park and plaza remain visionary: there's a beautiful riverside promenade, a rose garden with 1,400 rosebushes, and sculptures donated by member nations.

A 45-minute-long guided tour (given in 20 languages) is the main attraction; it includes the General Assembly, the Security Council Chamber, the Trustee Council Chamber, and the Economic and Social Council Chamber, though some rooms may be closed on any given day. Displays on war, nuclear energy, and refugees are also part of the tour; corridors overflow with imaginatively diverse artwork. Free tickets to assemblies are sometimes available on a first-come, first-served basis before sessions begin; pick them up in the General Assembly lobby. The Delegates Dining Room (PHONE: 212/963-7625) is open for a reasonably priced (up to $20) lunch weekdays (jackets required for men; reservations required at least one day in advance). The public concourse, one level down from the visitor entrance, has a coffee shop, gift shops, a bookstore, and a post office where you can mail letters with U.N. stamps. COST: Tour $10.50. Subway: 4, 5, 6, 7 to 42nd St./Grand Central.