William Trubridge, holder of 15 freediving world records, wrote: "I have a relationship with the depths, they beckon me beyond my means, cold dark vacant pressure, forever night, endless dreams." The 32-year-old New Zealander knows intimately the literal depths of the planet's waters.
With no fins, no tanks, no weights, no help whatsoever - nothing but a swimsuit and his own body and mind - Trubridge became the first person to swim alone straight down over 120 metres into the endless ocean, with only a vertical guide rope to pull himself down to the depths and back up to the sunlight.
If such an act of human endurance sounds incredibly extreme, that's because it is.
"The deepest dives last in excess of four minutes, but that's not four minutes of holding your breath in your bathtub - it's four minutes of propelling yourself through the water column, while combating pressures that would crush a soccer ball to the size of a tennis ball and exert mind-numbing narcosis on your neural circuitry," explains Trubridge, who holds a bachelor of science degree in physiology and genetics. "It's four minutes that takes place in another dimension, where time is drawn out into an eternity - an eternity that lasts but a single breath."
Freediving, meaning diving that is free of scuba tanks or any artificial breathing apparatus, is entering the mainstream like other formerly elite activities, such as skydiving, bungee jumping or kite surfing, already have. Like all extreme sports, the very element of danger is what makes freediving so intriguing. And with proper instruction and guided practice, anyone fit enough can experience this otherworldly discipline.
The last 10 years have seen a rapidly growing number of freediving schools and organisations around the world, as well as professional freediving competitions. For beginners, a wide selection of instructor-led freediving holidays are available in places as far-flung as Egypt, The Azores and the Philippines.
Trubridge teaches half a dozen courses in the Bahamas and Italy every year. He was the first to discover Dean's Blue Hole in the Bahamas, now recognised as the world's premier freediving venue and the place where he takes holidaymakers on freediving courses. Encircled by a natural rock amphitheatre, Dean's Blue Hole is the world's largest vertical sea cavern and plunges over 40 storeys down into the liquid depths. It's also the site of the annual Vertical Blue freediving championships, now in its fifth year.
But he's not the only freediving champion organising holidays. Former world record holder Umberto Pelizzari oversees freediving courses in the Red Sea and the Mediterranean. And four-time world-record holder Fred Buyle teaches freediving instructor courses in The Azores, in addition to hosting an annual freediving holiday on a live-aboard yacht in Greece's Saronic Gulf.
"Greece is an ideal location at the end of the summer. It's peaceful, the water is warm and the locations are stunning," Buyle explains. "I think a sailboat is the best way to experience freediving. Both activities are eco-friendly and, when spending a week on a sailboat, there's no need to worry about transfers to the dive site, losing time finding a place to eat and so forth. Everything is on site and people can spend more time with instructors too."
You don't need to be half-fish to enjoy a freediving holiday. Humans are biologically suited to the sport. Having floated in fluid for the first nine months of our lives, infants instinctively hold their breath for up to 40 seconds while making swimming motions when placed in water.
Since the 1960s, a scientific theory called the Aquatic Ape Hypothesis assumes that our ancestors evolved as part-time ocean-goers. Our lack of fur, our buoyancy, our supple spine, our insulating fat layers, and even our blood vessels and lungs are all adapted to life in the ocean.
"More and more people are quitting scuba diving to enjoy the freedom of movement and the silence of freediving," Buyle says.
"I'd compare freediving to a mix of hiking and rock climbing: If you just want to explore, you do sea-hiking, and if you want some physical component, you dive deeper."
Freediving may appear like some sort of macho sport for elite athletes. Not so, Buyle says. "Freediving is often perceived as a death-defying sport like base jumping. In fact, freediving is for everyone. There's no need to dive deep to have fun. The best dives are in the first 10 metres of water, where most of the sea life is and where the available light is at its best."
But for most first-time freedivers, the primordial feeling of being one with the ocean is a mystical seduction, and the depths of forever night and endless dreams always beckon one further.
The word ''apnea'' (derived from the Greek meaning ''without breathing'') is typically used when speaking about freediving as a competitive sport. Some freediving practices do not use any equipment, while others incorporate bi-fins, monofins, rope lines, and/or weights. Be sure to find out what kind of equipment is included with your course.
Breathing exercises for freediving may include underwater training in swimming pools, and even walking exercises while holding your breath. Breath control techniques should never be undertaken without supervision, as hyperventilation and lowered heart rates can lead to blackouts.
Scuba divers should never freedive between their tank dives, as decompression sickness – a potentially fatal condition also known as ''the bends''– may set in. Ensure that ocean freedives take place in uncrowded spots with plenty of quiet to focus.
Your freediving locale should be free of any strong currents, waves and tidal flows. And never, ever freedive without a diving buddy.
Confirm that the course is accredited with the International Association for Development of Apnea (also known as AIDA), an organisation founded in 1992 for freediving safety standards. SSI (Scuba Schools International) and FII (Freediving Instructors International) are two other reputable organisations for accredited freediving courses.
Vertical Blue (www.school.verticalblue.net) William Trubridge, the winner of the 2011 and 2012 World's Absolute Freediving Award, discovered the famed freediving spot Dean's Blue Hole in the Bahamas. He teaches freediving courses at that dramatic spot, and on the Italian isle of Elba and in Paris.
Apnea Academy (www.apnea-academy.com) Former freediving world-record holder Umberto Pelizzari, who practically wrote The Manual of Freediving, oversees ocean courses in places such as the Red Sea and the Mediterranean. He also runs accredited pool courses in Belgium, Germany, France and Spain.
Ocean Encounters (www.oceanencounters.net) Four-time freediving world-record holder Fred Buyle is now an environmental educator through his underwater photography and documentaries. But he still finds time to teach an annual freediving course on a live-aboard yacht in Greece's Saronic Gulf, and freediving instructor courses in the Azores.
Freediving-Philippines (www.freediving-philippines.com) Located on Cebu Island in The Philippines, this freediving school is run by Wolfgang Dafert, a longtime freediving instructor who helped pioneer the sport's new popularity in Asia. Two or three courses are run each month in Moalboal, with its dramatic coral wall and warm year-round waters.