Beaches
The park has four lovely beaches, each with its own personality: Espadilla Sur, Manuel Antonio, Escondido, and Playita. The prettiest is Playa Manuel Antonio, a small scimitar of coral-white sand with a small coral reef. It's separated from Playa Espadilla Sur by a tombolo--a natural land bridge formed over eons through the accumulation of sand--tipped by Punta Catedral, an erstwhile island now linked to the mainland. The hike to the top of Punta Catedral (100 meters) along a steep and sometimes muddy trail takes about an hour from Playa Espadilla Sur (also known as the Second Beach). Espadilla Sur and Manuel Antonio offer tidal pools brimming with minnows and crayfish, plus good snorkeling, especially during dry season, when the water is generally clear.
At the far right on Playa Manuel Antonio, you can see ancient turtle traps dug out of the rocks by pre-Columbian Quepoas. Female sea turtles would swim over the rocks to the beach on the high tide. The tidal variation at this point is as much as three meters; the turtles would be caught in the carved-out traps on the return journey as the tide level dropped. The people also used female-turtle decoys made of balsa to attract male turtles over the rocks. Olive ridley and green turtles still occasionally come ashore at Playa Manuel Antonio.

Wildlife Viewing
Between bouts of beaching, you can explore the park's network of wide trails, which lead into a swatch of humid tropical forest. Manuel Antonio's treetop carnival is marvelous, and best experienced by following the Perezoso Trail, named after the lovable sloths, which favor the secondary growth along the trail (perezoso means "lazy"). You might see marmosets, ocelots, river otters, pacas, and spectacled caimans in more remote riverine areas.

Howler monkeys languorously move from branch to branch, iguanas shimmy up trunks, toucans and scarlet macaws flap by. About 350 squirrel monkeys live in the park, another 500 on its outer boundaries. And capuchin (white-faced) monkeys are also abundant and welcome you at treetop height on the beaches, where they play to the crowd and will steal your sandwich packs given half a chance. Some of them have become aggressive in recent years and attacks on humans have been reported.
Even though it is illegal to feed the monkeys, insensitive people still do it. Note that if you're caught, you may--quite rightly--be ejected from the park. Recent studies have found a worrisome increase in heart disease and heart failure among the local monkey population. Unfortunately, the animals are much more prone to rises in cholesterol than humans. Do not leave food lying around.

Hire a guide. A guide can show you other interesting tree species--among them, the gaupinol negro, an endemic species that is in danger of extinction; cedro maria, which produces a yellow resin used as a traditional medicine; vaco lechoso, which exudes a thick white latex that also has medicinal properties, and the manchineel tree (manzanillo), or "beach apple"-- common along the beaches. The manchineel is highly toxic and possesses a sap that irritates the skin. Its tempting applelike fruits are also poisonous. Avoid touching any part of the tree. Also, don't use its wood for fires--the smoke will irritate your lungs.

Information
The park entrance is at the eastern end of Playa Espadilla, where you wade across the shallow Río Camaronera and pay your entrance fee ($6); little rowboats are on hand at high tide (30 cents), when you may otherwise be waist-deep.