Jumping from a 40-metre cliff, hoping your parachute will open; paddling out into huge seas and bracing as a three-storey wave crashes on your head.
Solo kayaking 23,000 kilometres past pirates and crocodiles from Germany to Australia; pulling up your body weight by one finger on a sheer rock face in Canada.
How can people do these things? And how can they overcome what would be paralysing fear for most of us, to seemingly cheat death?
Some say what they do is highly calculated to minimise risk and not an extreme sport, while others freely admit they are chasing that crazy adrenalin buzz, head down and charging.
Jaymz Hardwick — leaping off cliffs
Jaymz Hardwick has seen friends die BASE jumping, but said it was a misunderstood sport and not as risky as it seemed.
"It is dangerous, but it's not extremely dangerous. It's more a sport of the unknown," he said.
He rated wingsuit BASE jumping, where people jump off mountains in a bat-like suit and fly down at incredible speeds, as the most dangerous sport in the world.
While he does draw the line at that, he has jumped from a cliff barely 40 metres high, which many people regard as well below the safe limit.
Hardwick has done hundreds of BASE jumps and now focuses on the more technical challenges of the sport.
"It's a numbers game, that is you don't know when your time's up," he said.
Hardwick said he could bring himself to do such low jumps by calculating the risk to the finest degree.
He and his friends visited the site several times, measured the height and put in safety measures, including a rope system to ensure his parachute opened 1.5 metres after he started falling.
Fear was a big factor he used to his advantage.
"To us, fear is something that keeps you safe more than anything," he said.
"It allows you to check your pilot chute, check your pins, make sure that all your equipment is in check. Because in our sport equipment doesn't generally fail, it is human error. So that fear helps you double check, triple check."
He has had some close calls, like the time he jumped from Western Australia's 1099-metre-high Bluff Knoll, and a miscalculation saw him land in the trees. Luckily he wasn't seriously hurt.
The zenith of his career was when he was invited to a competition in Greece, jumping from huge, beautiful white cliffs overlooking the sea down to a landing spot on a small beach with a rusty shipwreck.
He plans to stop BASE jumping the moment his girlfriend becomes pregnant.
"I'd rather retire from this sport than unfortunately die from it," he mused.
Felicity Palmateer — riding massive waves
When Felicity Palmateer recently came off a 10-metre wave during a competition off the Hawaiian island of Maui, about 400 tonnes of water came pounding down on her.
And she enjoyed it — sort of.
"It's the strangest thing. There was nothing, no feeling going through me. I don't know how to describe it," the 25-year-old professional surfer said.
"It was like, I'm in the situation, there's nothing I can do, so let's just embrace it.
"I just really like the reward, you know — that feeling of adrenalin after catching an amazing wave or getting a big barrel.
"Even, as weird as it sounds, even wiping out, that adrenalin feeling after that, I kind of chase that feeling and it's inside you, you know, I kind of want to chase it. In those experiences is when you grow."
She does it because she has the drive that makes her want to take the drop on a lurching, heaving, beast of a wave. Not many do.
Palmateer puts it down to her father, who pushed her into bigger waves and told her to have no fear.
"I think if you have no fear, there's definitely something wrong with you," she laughed.
"I think anyone who says they're not scared when they're paddling out in 30-foot surf is lying.
"There's always going to be some little element of fear."
She has trained herself to be mentally comfortable in those extremely uncomfortable places, working on breathing exercises to give her more confidence in big surf.
And she has developed a mantra to calm her mind as huge slabs of ocean swell materialise on the horizon and threaten to push her deep under the water.
She thinks of a moment in her life when she felt really comfortable and happy.
"I literally shut my eyes in the surf and I just repeat that mantra, go over it again and try and get myself back to that. [To] have that same feeling again so my brain starts to make those same chemicals that it was when I was felling really happy and relaxed, and try and do that when I'm surfing 30-foot waves," she said.
Logan Barber — scaling rock faces
Logan Barber recently joined a short list of some of the world's best climbers when he became only the 12th person to climb Cobra Crack, a thin fissure up a vertical granite monolith in Squamish, Canada.
He has also travelled to remote locations in China, where he hung upside down from the Honeycomb Dome roof, the hardest traditional route in China, with stunning views of the wilderness behind him.
He is a traditional climber, which means he puts all his clamps and other gear into the rock as he goes, and removes it afterwards, without relying on any pre-existing bolts.
Barber has a calmness about him which makes you think he would barely break a sweat in the most terrifying climbing situations.
After years of experience, he said he felt no fear on the rock face.
"I wouldn't say adrenalin. When I'm climbing I don't really get scared or that buzz any more," he said.
"Generally, I'm pretty calculated, and I'm very focused on performing a routine."
"Once you're off the ground, you're in this vertical world and you're not really thinking about hitting the ground.
"You don't even know the ground is even there. You're just learning to fall. And when you fall, you've generally got a rope to catch you, whether it's after a metre or you might fall 15 metres.
"But, you know, the rope's there and you've calculated how you're going to land and you're ready to land."
He is completely focused on each new climb, but things can still go wrong.
He recalled one climb with a friend where after a couple of days they realised they were out of their depth and had run out of food, and had no choice but to keep going.
"You go a few days without food and you're just climbing a wall and you have to get to the top," Barber said.
"You basically get a bit lower on energy but you're still making sure you make the right decisions. You just keep doing what you know how to do, so eventually you know you'll get to the top. It's just a matter of how long."
"Things got a bit dire, but we kept going and we made it."
He felt he was at greater risk driving his car down the freeway and said it was rare to be in an uncontrolled situation climbing.
Sandy Robson — endurance paddling
Sandy Robson has always enjoyed endurance sports, including solo kayaking 23,000 kilometres from Germany to Australia.
It meant three years of paddling through Eastern Europe, the Mediterranean, the Middle East, Asia and through Papua New Guinea to Australian territory on Saibai Island in the Torres Strait.
The 49-year-old prepared by rehearsing everything that could go wrong.
"You really need to creatively visualise the worst-case scenarios that you might face and think about how you're going to respond so that you have an action, and if you don't have one you need to go out and practice until you've got it," she said.
That extended to her psychological approach to her fear of crocodiles.
She had previously been attacked by a crocodile during a trip to Cape York, and was told she needed to change her mindset to deal with the risk.
"So really rather than paddling along thinking that I'm prey and being fearful, [I learnt] to project my intention, which was to paddle to Australia and achieve this great goal," she said.
And that worked to an extent.
When she encountered crocs in PNG, adrenalin kicked in to get her through.
"Adrenalin is essential for you to be able to think and respond and act quickly and make decisions, but once it gets over a certain point, that's when it gets debilitating and I've experienced both of those in my time paddling," Robson said.
"Certainly when I was in the water and I had a crocodile chasing after my kayak, I was definitely at the peak there of, 'please don't get me, please don't get me.'
"You know, I don't think I was particularly efficient, but I got out of there fast."