Manuel Antonio National Park

Manuel Antonio is Costa Rica's smallest national park, barely 16 square kilometers, and its single busiest — proof that scarcity, not size, made it famous. What draws the crowds is a coincidence of geology found almost nowhere else on the Pacific: primary rainforest that grows in a straight, unbroken line down to white-sand coves, so that a troop of monkeys crossing the canopy overhead and a wave breaking on the beach can sit inside the same photograph. Titi trail and the Manuel Antonio beach loop are short and mostly flat, but the payoff density is unmatched in the country.

It holds three monkey species, including the Central American squirrel monkey — mono tití — a subspecies found only along this stretch of the central Pacific and nowhere else on Earth. Two-toed and three-toed sloths hang low enough in the fig and cecropia trees that a guide's spotting scope turns them from a rumor into a certainty within the first hour. Add white-faced capuchins working the trailside, howler troops calling across the ravines, and Playa Manuel Antonio itself — a half-moon of sand and reef curling inside the park boundary — and the appeal of a park this small stops needing an explanation.