Osa peninsula is home to Corcovado National Park, and endless wildlife, including more than 400 species of birds and more than 100 species each of amphibians and mammals. This tropical primary forest is home to monkeys, scarlet macaws, coatimundis and an abundance of other wildlife. It's not cheap, but taking a private charter flight into the Corcovado National Park for a day tour is well worth it.
The park is home to a plethora of endangered species such as Baird's tapir, the white-lipped peccary, jaguars, ocelots, crocodiles, giant anteaters, scarlet macaws and the harpy eagle. The seas shelter three species of marine turtles and you can even witness the migration of humpback whales in December and January.
On the other side of the peninsula is the Golfo Dulce, which is a sheltered area of ocean ideal for kayaking, visits to mangrove swamps or hiking and wildlife viewing at the Piedras Blancas National Park.
Finally, forest-covered Cano Island is a biological reserve which offers superb snorkelling and, for experienced divers, superb deep freshwater experiences with large schools of jacks, barracudas, manta rays and sharks.