Corcovado National Park is the largest stronghold of Pacific coastline primary rainforest, which has been all but destroyed from Mexico to South America. Its 41,788 hectares encompass eight habitats, from mangrove swamp and jolillo palm grove to montane forest. The park protects more than 400 species of birds (20 are endemic), 116 of amphibians and reptiles, and 139 of mammals—representing 10 percent of the mammals in the Americas on only 0.000101777 percent of the landmass.
Its healthy population of scarlet macaws (about 1,200 birds) is the largest concentration in Central America. Corcovado is also a good place to spot the red-eyed tree frog and enamel-bright poison-dart frogs. Corcovado is one of very few places in the country harboring squirrel monkeys. It’s also one of the last stands in the world for the harpy eagle.
Four species of sea turtles—green, Pacific ridley, hawksbill, and leatherback—nest on the park’s beaches. The park supports a healthy population of tapirs and big cats, which like to hang around the periphery of the Corcovado Lagoon.
Corcovado also has a large population of peccaries. Alas, the park’s mammal population—notably peccaries—is under intense pressure from illegal hunters and loggers.
The Osa Peninsula bears the brunt of torrential rains April–December. It receives up to 400 centimeters per year. The driest months, January–April, are the best times to visit.
Corcovado has a well-developed trail system, though the trails are primitive and poorly marked. Several short trails make for rewarding half- or full-day hikes. Longer trails grant an in-depth backpacking experience in the rainforest. Allow three days to hike from one end of the park to the other, which can be done in dry season only.
From La Leona: It’s 15 kilometers to Sirena, following the beach most of the way. Allow up to eight hours. Beyond Salsipuedes Point, the trail cuts inland through the rainforest. Don’t try this at high or waning tide: You must cross some rocky points that are cut off by high tide. Don’t trust the ranger’s statements—consult a tide table before you arrive. The hike from La Leona to the Madrigal waterfall is recommended.
From Sirena: A trail leads northeast to Los Patos via Corcovado Lagoon. Another trail—only possible at low tide (not least because sharks like to come up the mouths of the rivers in the hours immediately before and after high tide)—leads to the San Pedrillo Ranger Station (23 kilometers), at the northern boundary.
There are three rivers to wade. The trick is to reach the Río Sirena and slightly shallower Río Llorona before the water is thigh-deep. Here, watch for crocodiles. Don’t let me put you off; dozens of hikers follow the trail each week. Halfway, the trail winds steeply into the rainforest and is often slippery. The last three kilometers are along the beach. The full-day hike takes you past La Llorona, a 30-meter-high waterfall that cascades spectacularly onto the beach. Tapirs are said to come down to the beach around sunrise, but you must remain silent at all times, as the animals are timid and easily scared away.
From San Pedrillo: You can enter the park at San Pedrillo via the coast trail that leads south from Drake Bay, where lodges will also run you by boat. From the ranger station, a moderately demanding two-kilometer hike leads inland to a spectacular waterfall. Be careful, the rocks near its base are very slippery! It has pools beneath a cascade, good for bathing.
From Los Patos: The trail south climbs steeply for six kilometers before flattening out for the final 14 kilometers to the Sirena Research Station. The trail is well marked but narrow, overgrown in parts, and has several river crossings where it is easy to lose the trail on the other side. You must wade. Be especially careful in rainy season, when you may find yourself hip-deep. There are three small shelters en route. A side trail will take you to Corcovado Lagoon. Allow up to eight hours. Another trail leads from Los Patos to Los Planes.
A basic bunkhouse with foam mattresses (but no sleeping bags or linens) is available at Sirena ($8 pp), where there are showers and water; reservations are essential via the Corcovado park headquarters in Puerto Jiménez . Rangers will cook meals by prior arrangement ($15 breakfast, $20 lunch and dinner), but you have to supply your own food.
Camping is allowed only at ranger stations ($4 pp). Rangers can radio ahead to the various stations within the park and book you in for dinner and a tent spot. No-see-ums (pesky microscopic flies you’ll not forget in a hurry) infest the beaches and come out to find you at dusk. Take a watertight tent, a mosquito net, and plenty of insect repellent. You can rent tents and stoves in Puerto Jiménez from Escondido Trex.
Reservations are required for overnight (30 days’ notice is recommended due to limited space); prepayment is required through Banco Nacional.
Corcovado National Park has four entry points: La Leona, on the southeast corner near Carate (the ranger station is about two kilometers from Carate); Los Patos, on the northern perimeter; San Pedrillo, at the northwest corner, 18 kilometers south of Drake Bay; and Los Planes, on the northern border midway between San Pedrillo and Los Patos.
You can also fly into the park headquarters at Sirena, midway between La Leona and San Pedrillo. All are linked by trails. Entrance costs $10 (maximum four nights), prepaid at Banco Nacional.
The park is administered through the Osa Conservation Area headquarters in Puerto Jiménez (tel./fax 506/2735-5036, pncorcovado [at] gmail [dot] com).
You can charter an air-taxi to fly you to Sirena from Puerto Jiménez  with Alfa Romeo Aero Taxi ($500 up to five people). Otherwise you’ll have to hike in from Carate or one of the other access points.
Boats from Marenco and Drake Bay  will take you to either San Pedrillo or Sirena.