Atlantic Rainforest
Rio de Janeiro has the biggest green area within a city in the world. It is called Tijuca Massif and a smaller part is the Floresta of Tijuca, the Tijuca Forest. The whole area is covered with Atlantic Rainforest and protected by the IBAMA, the Brazilian environmental agency.
There are various peaks that can be hiked up and the duration of the excursions varies between a couple of hours and a whole day.