A place of swaying palms and playful monkeys, sparkling blue water and a riot of tropical birds, Parque Nacional Manuel Antonio is the country's smallest and most popular national park. It became a protected area in 1972, preserving it from being razed to make room for a coastal development project. It's a truly lovely place; the clearly marked trail system winds through rainforest-backed white-sand beaches and rocky headlands, the wildlife (iguanas, sloths, monkeys) is plentiful, and the views across the bay to the pristine outer islands are gorgeous.
The downside? Crowds. Visitors are confined to around 6.8 sq km of the park (the rest is set aside for ranger patrols battling poaching) and the place gets packed when midmorning tour buses roll in. Get here early (7am) and head for the furthest reaches of the park for a bit of tranquillity and the best chances to spot wildlife.