Praça XV de Novembro is the oldest square in Rio and the historic heart of the city, fronting Guanabara Bay at the point where the original Portuguese settlement was established in 1565. The Paço Imperial, the former royal palace on the square's edge, is now a cultural centre with free exhibitions and a good restaurant.
The surrounding streets — Rua do Ouvidor, Rua Primeiro de Março, the covered Travessa do Comércio — form Rio's best-preserved colonial neighbourhood, with 18th- and 19th-century buildings housing banks, law firms, and a few atmospheric restaurants and bars. The square is also the departure point for ferries to Niterói and the Ilha Fiscal. Worth half a morning to explore before the midday heat; combine with the Museu Histórico Nacional and the Real Gabinete Português de Leitura.