The species list reads like an inventory of everything the tropics can produce. The jaguar population here is the healthiest in Central America, though sightings remain extraordinarily rare -- most locals who have lived near the park their entire lives have never seen one. Pumas, smaller and more arboreal here than their North American counterparts, share the forest with ocelots, jaguarundis, and margays. Hundreds of Baird's tapirs live within proximity of Sirena Station, often found lounging in shallow pools or ambling through the shade. The birdlife includes over 350 species: scarlet macaws flash through the canopy, chestnut-mandibled toucans perch in fruiting trees, and the critically endangered harpy eagle hunts somewhere in the forest interior. On the ground, fer-de-lance vipers -- called terciopelo locally, or more colorfully "Costa Rican landmines" -- hunt along streambeds at night. Two species of peccary run in packs aggressive enough that the standard advice for an encounter is to climb a tree and wait six feet off the ground.

Nothing about reaching Corcovado is casual. The most accessible trail, Sendero El Tigre near Dos Brazos de Rio Tigre, is an eight-kilometer loop that takes six to eight hours. From the south, the hike from Carate to La Leona ranger station covers 3.5 kilometers of beach before you even enter the park. The sixteen-kilometer trek from La Leona to Sirena Station follows a route that alternates between beach and trail, and visitors must time their arrival at a river crossing two kilometers from Sirena to coincide with the lowest tide -- the Rio Sirena holds crocodiles and bull sharks. From Los Patos to Sirena, it is twenty kilometers through secondary rainforest, roughly eight hours of walking. The longest route, San Pedrillo to Sirena, stretches twenty-nine kilometers along the beach with almost no shade, though most of that trail has been closed since 2009. Drake Bay, on the park's northern side, provides boat access that bypasses the worst of the overland approaches.

One of Corcovado's most striking features is the way its rainforest grows directly to the ocean's edge. There is no gradual transition from jungle to coastline -- the canopy simply ends where the sand begins, and the density of life on either side of that line is staggering. Natural rock formations, waterfalls, rivers, and beaches break up the forest without diminishing it. Sirena Station, the park's central hub, sits twenty kilometers from each entrance and serves as the primary base for multiday explorations. It is the only station offering dormitory lodging and hot meals in addition to camping. La Leona, San Pedrillo, and Los Patos offer only campsites with no food service. Backcountry camping is prohibited within park boundaries to protect the fragile ecosystem, though it is permitted outside the park for adventure trekkers willing to navigate routes that once connected Carate to Puerto Jimenez before bush planes made the journey unnecessary.

Corcovado demands preparation that most national parks do not. The park recommends a bare minimum of 1.5 liters of water for the La Leona to Sirena hike, but experienced hikers carry at least three -- dehydration and heat exhaustion in this environment can kill quickly. Swimming in the ocean is dangerous due to powerful tides, and the rivers hold crocodiles, bull sharks, and caimans. Permits must be reserved in advance and cannot be obtained more than one month before arrival. The park service accepts payment only through in-country bank deposits, a bureaucratic reality that adds logistical complexity to an already challenging trip. Roads on the Osa Peninsula require four-wheel drive, and the route from Puerto Jimenez to Carate involves river fordings that should only be attempted in dry season. All of this difficulty is, paradoxically, what keeps Corcovado extraordinary. The park has remained so biologically intense precisely because it has remained so hard to reach.