Swimming as a sport received quite the boost in recent years thanks to Olympic performances by Ryan Lochte and Michael Phelps, not to mention the accompanying stories about their insane workout routines and diets, respectively. Yet beyond sprints and relays there remains another side to the sport, popular mostly with triathletes, endurance junkies, and the occasional band of prisoners: open water swimming. You thought a long-distance run was tough? Try swimming 20 miles, in cold water, with ocean swells, strong currents and sharks. Here are 10 of the most challenging open water swims. Some are races, some are destination swims, and some are nearly impossible.

MORE SWIMMING: Escaping from Alcatraz | A Return to the Wreck | Road to Ironman

Norseman Xtreme Triathlon

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Hardest Triathlon Swim: The swim leg of a typical Iron-distance triathlon (2.4 miles) is no breeze, but drop competitors 12 feet from a ferry into a fjord that averages 57°F on race day and it becomes downright hard. Instead of hot cocoa, triathletes at Norseman emerge from the water for a nice hot cup of 138 more miles on bike and foot, 15,000 feet of elevation gain, and a finish line at the peak of Gaustatoppen — which shares the latitude of Anchorage, AK — where it just might be snowing.

Waikiki Roughwater Swim

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Most Exciting: Want to go for a long swim and relive a bit of sports history? The Waikiki Roughwater Swim was the original swim leg for the Ironman World Championship, which from 1978-1980 was held on Oahu (it’s now held on the Big Island). The race is a point-to-point from the base of Diamond Head volcano to the Hawaiian Village, covering 2.4 miles of Oahu’s southern coast. Look out for choppy water, strong currents, and hundreds of other swimmers rubbing shoulder to shoulder.

Manhattan Island Marathon Swim

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Hardest City Swim: New York City is one of the great financial and cultural capitals of the world, and it turns out the same is true for open water swimming. Dating back to the 1920s, MIMS is today considered one of three most important open water swims, along with the English Channel and the Catalina Channel, for those who keep track of such things. The field is limited to 25, which makes sense considering it’s 28.5 miles around the island, with water temperatures in the 60s, along with choppy water, boat traffic and floating debris — not to mention a $2,000 entry fee.

Farallon Islands to Golden Gate Bridge

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Best Assortment of Wildlife: Swim from the Farallon Islands, 30 miles off the coast of San Francisco, to the Golden Gate Bridge and you’ll in be in good company: only two people have ever done it. The swim starts off the coast of South Farallon, a National Wildlife Refuge since 1969, and proceeds through cold water (in the 50s), massive swells, powerful currents, and aquatic wildlife including seals, whales and great white sharks. Oh, and no wetsuits are allowed, according to the Farallon Islands Swimming Federation.

Robben Island to 3 Anchor Bay

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Best Prison Break Swim: Part of the allure of open water swimming is the feat of covering long distances with only human-powered propulsion. It’s audacious. And what could be bolder than attempting a prison break from an island? Only one prisoner ever escaped from Robben Island Prison, 4.3 miles off the coast of Cape Town, South Africa. That was Autshumato, an interpreter for the first Dutch settler, and it was 350 years ago. Nelson Mandela spent many years imprisoned in Robben Island, but today the prisons have closed and the only attempts to escape are made by ambitious swimmers who paddle from the island to Three Anchor Bay, a 6.3-mile swim through chilly water.

English Channel

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Most Iconic Open Water Swim: Short of doing it in a modified Nissan pickup like the gentlemen at Top Gear, the most eccentric way to cross the English Channel is by swimming. It’s also arguably the most iconic of open water swims, dating back to 1875 when Captain Matthew Webb swam from England to France across the Strait of Dover (20.7 miles, if you stay on course), unassisted, in 21 hours 45 minutes. Today, Channel swimming is tightly regulated because of the high traffic in the Strait and the number of people who want to attempt the swim. If you want to attempt it you’re looking at a few years on the a wait list, $3,700 dollars for a support boat, and proof of a six hour swim in cold water.

Ice Swimming

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Craziest Swim: Though not a race or organized event per se, ice swimming ranks high on the list of challenging open water swims. The sport’s governing body, loosely speaking, is the Cape Town-based International Ice Swimming Association, and the way to get in is to swim at least one mile in water measuring below 41°F, without a wetsuit, and provide video and photo proof thereof. The founder group’s founder, Ram Barkai, set the Guinness Book of World Records mark for the most southerly swim in Antarctica, swimming one kilometer in water measuring 1°Celsius… if you needed some inspiration.

Loch Ness

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Swim Most Likely to Include Monsters: The swim across Loch Ness in the Scottish Highlands ranges from extremely difficult — 23 miles in length, cold water, near zero visibility — to harrowing, should you encounter the lake monster that allegedly resides down deep. The good news is the beast hasn’t claimed a victim, ever, and there’s plenty of real estate in Loch Ness, which is 750 feet deep and 685 square miles, for everyone to get a swim in. Competitors who want to get a taste of Loch Ness but not put in the full 23 can enter the yearly Loch Ness Monster swim, which is just one mile.

Straits of Florida

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Swim Most Necessitating a Cage: We’ve been to Key West. Cuba, too. But a swim between the two is the provenance of either a politically incorrect joke or — well, that’s pretty much it. Empirically, the roughly 100-mile swim is nearly impossible, if not from the 24 hours or more of continuous swimming and strong currents, then from the sharks and jellyfish lurking below. In fact, the feat has been accomplished just once, in 1997, by Australian distance swimmer Susie Maroney, who swam in a cage to protect her from debilitating stings and bites; many others have failed, including another Aussie, Chloe McCardel, who made the attempt in 2013 but got knocked out by a pack of obdurate jellyfish.

[Update: On September 2, 2013, swimmer Diana Nyad completed this swim without a shark cage. She is 64 years old.]

Alcatraz Swim

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Editor’s Pick: The trip from the most infamous federal penitentiary in American history to the shore in San Francisco may not be as physically demanding as the Robben Island swim, but what it lacks in distance it makes up in lore: three prisoners escaped the The Rock in 1962, never to be found, a story recounted in Escape from Alcatraz starring Clint Eastwood. (Not even to mention the Michael Bay movie with Nic Cage as weapons expert Stanley Goodspeed.) GP’s own Jason Heaton has completed this swim. In his words: “The distance amounts to about a mile and a half, the equivalent of about 90 lengths of the pool at your local YMCA. Spend enough lunch hours putting in your laps and the distance is doable. But factor in strong current, waves, cold water, shipping traffic and San Francisco’s chilly weather, and Alcatraz is considerably more formidable. And then there’s the psychological challenge — what lurks beneath you in that dark, cold water?” Find out yourself.