Parque Penhasco Dois Irmãos

Many places in Rio provide lovely vistas but are outside the usual tourist trek.
This park is located at the end of Leblon and provides a lovely view over the Lagoa Rodrigo de Freitas, Ipanema and Leblon beaches, all the way to Copacabana.
Access it by car (or a long walk) up the Rua Igarapava, which in turn starts on Rua Visconde de Albuquerque, which runs along the canal