In Costa Rica's Corcovado National Park it's just you and the jungle-and the pumas, scorpions, and white-lipped peccaries

There are many reasons not to go bushwhacking in the jungle at Corcovado National Park in Costa Rica: deadly fer-de-lance snakes, stinging scorpions, herds of teeth-gnashing, white-lipped peccaries (similar to wild boars), ticks so tiny you can barely see them as they embed themselves in your ankle and other less obvious places, trees with sharp thorns that can pierce your shoes, and-of course-the enormous potential for getting completely, utterly lost.

But we had one motivation that overrode all these fears: the tide was lapping at our heels. My three companions (an American and two Israelis) and I had just trudged down a torrid beach in the raging sun, feet sinking with every step, after plodding about six kilometres along a saunalike jungle path. The sweat was running down my nose in rivulets, so much that I was trying to catch it with my tongue to use as drinking water. The wild, crashing waves were an oasis in the desert; they looked refreshing and cool, but we couldn't go in. If the sharks didn't get us, the notorious undertow would. "We lost a backpacker about a month ago," the ranger had warned us at the La Leona station as we entered the park.

Now we were confronted by a rocky headland with no discernable path. None of us had a map, but when I checked later I guessed it was Punta Salsipuedes, which translates roughly as "Leave-If-You-Can Point".

The American climbed up the steep slope into the jungle and yelled down from the top of the cliff, "I think I've found a path-sort of."

His confidence was underwhelming, but we had no choice unless we wanted to hike about 10 kilometres back to La Carate, where we had begun our adventure at 8 a.m. after a gruelling two-hour colectivo ride on dirt roads from the sweltering town of Puerto Jiménez. (A colectivo is a shared taxi, in this case a covered truck in which passengers sit on benches in the back.)

I scrambled up the sheer mud cliff, grasping at roots and trees to hoist myself. The two Israelis followed. At the top, one of them veered off into the underbrush, shouting, "I'm just going to look over here."

He vanished in seconds. We couldn't see him; we couldn't hear him. Silence welled up as we sweated. Visibility in the jungle is about 30 feet, once you get away from the path.

A few minutes later, he called to his friend in Hebrew. "Did he find the path?" I asked. His companion gestured to us to come, so we slogged farther away from the coast, every step a chore in the dense greenery. We found him in the jungle, no sign of a path anywhere. A fury of words erupted.

"I said I found a way. What are you doing running off into the jungle like that?" the American yelled.

"It sure didn't seem like a path," the Israeli countered.

"It's better than just going into the jungle. Let's go back to it; at least that way we'll be near the coast." The Israelis agreed, and tromped ahead in the brush.

A few seconds later, I lost my footing on the slope and slid into a fallen tree, spikes on its trunk puncturing my soft hiking shoes. Further ahead, one of the Israelis let out a shout of joy, "The trail. I see the trail!"

We were saved. Only another seven kilometres to go.

Hiking Corcovado can be hard-core. The hikes themselves aren't that hard, just long, but the heat-temperatures of 27 to 35?° C-and the suffocating humidity conspire to suck the life right out of you. I drank three litres of water during the first day and would have had more if there was any left. Most visitors hike on the beach from where the road ends at Carate past La Leona ranger station to Sirena ranger station (about 18 kilometres) and through the jungle from Sirena to Los Patos ranger station (20 kilometres), plus another three kilometres to the road, or vice versa. It is also possible to hike farther along the coast to the San Pedrillo ranger station, but only during the dry season (January to May) and when the tides are favourable.

If you can ignore the heat, health hazards, and discomfort, you will find you've arrived at one of the most astounding places on Earth. Corcovado is biodiversity. Tucked away on the Osa Peninsula in southwest Costa Rica, this national park is home to about 500 species of trees, 140 mammal species, 367 bird species, 6,000 insect species, and 117 different reptiles and amphibians, including the extremely toxic poison-dart frog. Endangered species like the puma, Baird's tapir, the American crocodile, the ocelot, and the jaguar find sanctuary here. In my three-day trip, I saw all four species of monkey found in Corcovado: howler, spider, squirrel, and the white-faced capuchin. The largest population of scarlet macaws in Costa Rica resides in the park. As we started our hike, at least 15 of the majestic, squawking birds swooped over us on the beach. I also saw countless lizards, which look disturbingly like small snakes as they scuttle quickly off into the undergrowth; occasionally, they really were small snakes. Then there was the pack of raccoonlike coatis with babies, several agoutis (which look like giant rats), and crocodiles in the Rio Sirena, a short hike from the Sirena ranger station.

After we found the path, we began to focus on making time. The hike had gone from unpleasant to miserable, and dehydration was making us all testy. Finally we reached the Rio Claro, the only place after La Leona where it is safe to swim; the caimans in the water are, apparently, harmless. The tide was coming in and we had no choice but to get wet as we forded the waist-deep river, trying to hold our packs above. Swimming was so mercifully cool and refreshing I could barely stand it. But we couldn't stay long. It was already 5 p.m., and the sun would go down at six. You can't see snakes in the dark.

After five minutes of walking, I was covered in sweat again, the river a distant memory. We were out of water. When the path reached the airstrip and we could see the Sirena station, the two Israelis kissed the ground.

The next day, I set off alone at 6 a.m., aiming to beat the heat for the 20-kilometre hike through the jungle to the Los Patos ranger station.

An agouti scampered off into the bushes as I entered the jungle trail in the early-morning light. The haunting, thunderous calls of howler monkeys echoed in the distance. Other noises, which I had never heard before, made me uneasy. When you are alone in the jungle, you notice things: you hear every foreign sound and you jump at every rustling of the bushes. If something goes wrong, it's just you and the jungle.

I made tracks at a frenetic pace. Trees towered to impossible heights over the path; giant ferns grew in the underbrush. Phantom snakes were everywhere. Horseflies dogged me almost the entire way, circling my head. The buzz of a hummingbird caught my attention as it hovered briefly over a small creek pouring through an immense gorge in the rocks. I watched basilisk lizards, called "Jesus Christ lizards" by the locals, run on another river, seeming to fly. Squirrel monkeys approached me in the forest. Small and tiny with seeming wizened, old heads, they came disturbingly close to pose for pictures, though I suspect they were really looking for potato chips.

Farther on, spider monkeys vented their wrath, shaking the branches so a shower of leaves descended upon me. Toucans and parrots squawked overhead, but I had no more patience for bird watching. By the time I stumbled into the Los Patos ranger station at 2:30 p.m., I was so exhausted I could barely speak English, never mind Spanish. I had to wait until the next morning for the colectivo back to Puerto Jiménez, which picks up three kilometres from the station. I was wet, icky, covered with bug bites, and carrying a few ticks.

Overnight, it rained. "The colectivo might not come today if the river is too high," the ranger warned. But nothing could stop me from trying. Making my way down the slippery path to the river, I fell over like a turtle, flat on my back, so weighted down by my pack that it took me a few minutes to figure out how to stand up again.

When I reached the river, I felt lost. I couldn't envision how a car could possibly come there. The road seemed to vanish before and after the river, going nowhere. I dropped my pack and waited as the mist became drizzle and the drizzle became rain. Howler monkeys flew through the trees near the river. It felt like a crossroads between this and some other world, so misty and mysterious and devoid of any signs of civilization.

And then I heard the welcome sound of a motor far off in the bushes on the other side of the river.

Even the colectivo was an adventure. The driver said we'd cross the river 24 times before reaching the town of La Palma, where the road becomes a real road. "Crossing" the river meant driving through it. As we roared through again and again in a mini-monsoon, visions of clean, relatively bug-free bed sheets and hot showers warmed my brain.

ACCESS: Puerto Jiménez is located in the southwest corner of Costa Rica, some 370 kilometres from San Jose. For about US$80 one way, both Sansa and Travelair offer one-hour flights to Puerto Jiménez. Bus fare is about US$8 per person and takes about nine hours, if you are lucky. From Puerto Jiménez, colectivos (expect to pay US$6) take hikers to Carate, where the road ends (but only in the busier, drier months, from January to May). It's also possible to catch a colectivo from Los Patos, though service here is less reliable. Otherwise, you can hire a taxi.

The entrance fee at Corcovado is US$8, and camping costs $4 a day. Dorms are available for US$8 a night at Sirena and Los Patos.