Corcovado National Park is Costa Rica’s most spectacular national park

Corcovado is a good place to spot the red-eyed tree frog (listen for his single-note mating "cluck"), the glass frog with its transparent skin, and enamel-bright poison-arrow frogs. And you can watch fishing bats doing just that over rivers at night. You can even try your own hand for snook inside the mouths of the coastal rivers on incoming tides. They strike plugs all year and during the fall become very aggressive. Corcovado is one of only two places in the country that harbor squirrel monkeys (the other is Manuel Antonio). It's also one of the last stands in the world for the harpy eagle, although it hasn't been seen here in the last several years and may now be extinct in Costa Rica.

Source : centralamerica