What is too extreme? That was a common question among vacationers—and others for that matter—in the wake of the deadly volcanic eruption in New Zealand in December. To be sure, many of those exploring White Island last year didn't think they were putting themselves in danger. But for some adventurers, danger is exactly the point; in fact, there is a whole category of vacations custom-designed for extreme thrill seekers.
"Our clients are looking for high-adrenaline experiences, something that gets their heart pumping," says Geordie Mackay-Lewis, co-founder of Pelorus, a London-based travel company that designs individualized adventures. Adds co-founder, Jimmy Carroll: "For one group, we created a drug trafficking plot in Cambodia. It started with urban surveillance training in Siem Reap and then moved into the jungle to track an international arms gang, who chased them with guns, to a helicopter that transferred them to safety."
Why do some people seek death-defying adventures like freefalling off a cliff, diving with crocodiles or even volunteering to be kidnapped, while the risk threshold for others goes no farther than reading the latest thriller on a private beach?
It seems the predilection for thrill-seeking and risk-taking is all part of our DNA. The late Dr. Marvin Zuckerman, a Professor Emeritus at the University of Delaware, was known for his research involving the sensation-seeking trait that suggests that it's hardwired in our genes whether or not we crave novel and thrilling experiences and how susceptible we are to boredom. High sensation seekers tend to seek out stressful jobs such as firefighting and and working in emergency rooms, and in turn also seek out extreme and risky experiences such as skydiving and bungee jumping.
The good news for these high-sensation seekers is that when they want to take a vacation from the high-stress jobs they probably have, there are travel companies catering to their preferences with equally high-stakes adventures.
Read on for some more options—fair warning, they are not for the faint of heart.

Navigate the Jungle Alone
Naked and afraid? Not if you have your wits about you on this true-to-life survival adventure in the remote jungle of Guyana, South America. You'll be dropped alone—or with a buddy—in the jungle for a week with no more than the clothes on your back, a machete, bow and arrow, and a few days of survival training. Thirty percent of participants pull out of the experience during the training phase. Can you make it all the way? Bushmasters also offers other realistic, survival expeditions to remote and harsh destinations including the Amazon jungle and the Arabian Desert.

Heli-Bike in Alaska
In the summer and fall, you can now try heli-biking. Olympic Gold Medalist Tommy Moe and fellow heli-ski veterans devised the country's first helicopter outfitted with a bike rack. It allows cyclists of all ages and levels and their bikes to be flown deep into the Tordrillo Mountain Range and dropped down into remote Alaskan trails carved in the flanks of area volcanos. Or you can forge a brand-new path on a glacier.

Play Survivor on a Deserted Island
Be a castaway for 10 days on an uninhabited island in French Polynesia, Tonga or Panama with a tribe of strangers from around the world. You'll learn bushcraft survival skills for the first half before putting them to the test when left to your own devices for 72 hours before you're rescued.

Sail the Drake Passage
Forget merely crossing the most dangerous sea in the world, try sailing it. Also known as the Mar de Hoces and famed for its treacherous crosscurrents and high winds, the Drake Passage's 600-mile stretch between Antarctica and the southern tip of South America isn't for the faint of heart, even on a more traditional cruise ship. Sail to Antarctica on Bark Europa's tall-ship and you'll have to hold on extra tight.

Compete in a Suspense Thriller
Mackay-Lewis and Carroll of Pelorus are two ex-British army captains. They'll let you safely live out your own action-packed suspense thriller with their team of actors, as well as by tapping Special Forces and intel agency experts to develop simulated escape-and-evasion or espionage missions. You'll see how you would react and negotiate in high-pressure, your-life-might-depend-on-it situations. And you'll have major bragging rights when talking about what you did on your vacation.

Conquer Europe's Highest Peak
Forget the crowded lines at Everest and instead summit Mount Elbrus in the Russian Caucasus Mountains. Considered to be one of the more accessible of the "Seven Summits," the tallest mountains on each continent, Elbrus towers at 18,510 feet. Adventure companies such as WHOA (Women High on Adventure) lead expeditions to Elbrus' breathtaking peak that include on-site mountaineering training—including how to self-arrest with an ice ax (a technique to stop yourself from freefalling down steep, icy slopes).

Be a "Top Gun" Pilot
Leave it up to the country with the oldest policy of military neutrality in the world to come up with flying a real fighter jet for fun. Swiss aviation enthusiasts at MiGFlug offer flight experiences in locations around the world. Sitting in the cockpit beside a highly trained fighter pilot—and often holding the controls yourself—you'll try out aerobatic maneuvers like spins and barrel rolls, negotiate between mountain peaks, and in one experience, you can even participate in an aerial dogfight.

Dive with Nile Crocodiles
For upwards of $20,000 per person, Big Animals Global Expeditions takes you diving in Botswana with African crocodiles, the second largest living reptile in the world. While these crocs have bites more powerful than those of a great white shark, the good news is that the cold water makes these predators lethargic, and their poor underwater vision might let you sneak a photograph or two from as close as 12 inches away.