Instead of the beaches, visit rooftop pools in Rio.
If you are looking for a good pool to check out head to the Marina Palace Hotel in Leblon.
The ideal afternoon includes a hike in the Dois Irmaos Park, which is a pretty steep uphill climb but with plenty of stops along the way. There is a beautiful monument to remember the victims of the Air France flight 447 crash half way to the top.
Post hike, return to the Marina Palace Hotel for cocktails on the roof - which you can enjoy even if you aren't a guest - swim in the infinity pool and love Rio for everything it offers.