The Top Ten Extreme Adventures (cont.)

5. Run the Adventure Circuit in Borneo
Not sure what you want out of an adventure? Jungle, mountains, rivers, caves—or perhaps that ever-elusive "all of the above?" This 15-day excursion with World Expeditions ranges from Borneo's most famous underground lair to its highest peak, and many highlights in between.

The underground nether-world of Sarawak, in Mulu National Park, is one of the world's largest limestone cave systems and contains the biggest cave chamber on the planet. From those clammy depths you will, eventually, ascend 13,435-foot Mountt Kinabalu.

In between, hike to the Pinnacles, razor-sharp rock formations, and trek deep into steamy rainforest to spy orangutans, proboscis monkeys, and countless colorful birds. Sarawak and Sabah harbor thousands of plant species, including the rafflesia—the world's largest flower, spanning up to three feet in width.

4. Trekking in Papua New Guinea
To see the last vestiges of the Stone Age, put down the TV remote and get your butt to the viney jungles of Papua New Guinea. Papua Trekking's two-week hikes bring clients face to face (or, um, CoolMax to loin cloth) with dwarf tribes, stone-tool makers, tree people, and villages that only recently gave up cannibalism.

The hikes, deep into the jungles of New Guinea Island and Irian Jaya, are moderately demanding and require a love of adventure; these are not staged acts where the players don Nike shirts the minute you leave. In fact, the trekking groups occasionally still encounter people who have never before seen a Caucasian.
Papua New Guinea Vacation Guide

3. K2 Exploratory Trek
In the pantheon of mountaineering lore, there are the Himalayas and there is everywhere else. This trip with World Expeditions takes you onto the northern flank of K2, the second highest peak in the world. You aren't climbing K2, "only" walking up to base camp (at 17,388 feet above sea level), but that should be enough to convince you that, as many mountaineers insist, this is the most scenic alpine environment on earth.

This is a first-time offering for World Expeditions, which means the itinerary could change and participants may need to improvise. But the group has an experienced hand leading the trek: two-time Everest summiteer Tim Macartney-Snape.

The journey begins with a road trip from Kashgar, China, to Xinjiang, and onward through dizzying scenery to Elik. Then the walking begins, through Kyrgyz settlements, multiple river crossings, steep gorges and valleys, and, further up, the Great Mountain.

From base camp you'll have ample time to gawk at the summit of 28,251-foot K2—and gather wisdom from Macartney-Snape, who has spent months of his life in the region—before retreating to reality.
Outside magazine's K2 Archives

2. Ski the Last Degree in Antartica
You've safely assumed that skiing in Antarctica does not involve chairlifts, condos, or a thriving après ski scene. So what does it entail? Focus, perseverance, and more self-locomotion than most people generate in a year.

The ten-day trip with Alpine Ascents also offers bragging rights to an accomplishment that was once reserved for only of a handful of explorers: skiing to the geographic South Pole.

Fly to the 89th longitudinal degree then set off on cross-country skis over undulating, chalk-white terrain in weather that could be cheery and crisp or March of the Penguins bleak. The prize, after 70 miles, is the chance for a photo op at the bottom of the world—the 90th degree, where the ice beneath your skis is almost 10,000 feet thick.
Antarctica Vacation Guide

1. Amazon Jungle Trek and Survival Training
If your childhood dreams featured full-tilt exploration, whacking through brush with a machete, and the thrilling uncertainty about what lurked around the next bend, this one's for you: a three-week expedition-cum-survival-training course in the trail-less heart of the Guyanese Rainforest.

You'll be toting a 50-pound pack with a machete and survival gear but, oddly, no food.

"We live [mainly] off fish, which we catch as we go," says Ian Craddock, who leads the expeditions for the outfitter Bushmasters. "Everyone needs to know how to do this, with hook and line, bow and arrow, sometimes with natural poisons from vines. Of course our staff show them how and help out."

Hike seven hours a day with rest stops and lunch—and the occasional river crossing or cliff rappel—and doze hard at night in a hammock with a small shelter tarp. Other survival skills taught: making fire without matches and milking water from vines.

It's not all work: The jungle offers solitude, encounters with indigenous tribes, and sightings of anaconda, jaguar, massive tarantulas, and, says Craddock, "thousands of birds." That's worth a little effort, no?