One of the most beautiful modernist structures ever created (designed by Oscar Niemeyer with landscaping by Burle Marx and detailing by Milton Ramos), the Palácio do Itamaraty now serves as a ceremonial reception hall for the Department of Foreign Affairs. The interior is a match for the outside, so it's worth taking the tour. The ultramodern structure -- mostly open space inside -- is decorated with rich antique furnishings of Persian carpets, hand-carved jacaranda-wood furniture, and 18th- and 19th-century paintings. Somehow it really works. Guided tours only. Call ahead to request an English-speaking guide.