A marathon is a very hard thing to do, but there are ways to make it even harder. For instance, you could run it underwater, with a belly full of wine, or at a few thousand feet up in the world's highest mountains.
We've rounded up seven of the planet's wackiest, weirdest and toughest marathons, from all corners of the globe – races in which you'll not only run 26 miles, but also question your own sanity. It's absolutely guaranteed – if you do these races, you'll want to keep the T-shirt. On your marks, get set, go.
More: 7 wacky world records you'll never believe
1. Everest Marathon
Location: Gorak Shep, Nepal
Challenge level: 8
Dangers: Altitude sickness, pulmonary oedema, hypothermia
Differentiator: The world's highest marathon
Record time: 3h40m43s – Ram Kumar Raj Bhandari (Nepal), 2013
Competitors must hike for 15 days just to get to the 17,000-foot start of this marathon, and organizers recommend climbing two 18,000-foot mountains en route to acclimate.
The run from Gorak Shep to Namchee Bazaar (11,306 feet) is mostly downhill, but also has two steep uphill sections and unusual hazards such as rickety suspension bridges and yak trains.
2. Great Wall Marathon
Location: Tianjin, China
Challenge level: 6
Dangers: Tripping, disorientation
Differentiator: Includes 5,164 steps
Record time: 3h9m18s – Jorge Maravilla (USA), Dimitris Theodorakakos (Greece) and Jonathan Wyatt (New Zealand), 2013
This step-filled challenge is brutal on the legs, with over 5,000 steps as it passes up, over, along and around the Great Wall of China.
Mostly run through traditional villages on the Huangya pass, it also involves 3.7 miles on the Tianjin section of the actual wall – but that painfully consists of two runs on the same stretch. Miss the six-hour cut-off and you can't go back up.
3. Safaricom Marathon
Location: Lewa Wildlife Conservancy, Kenya
Challenge level: 3
Dangers: Animal attack, sunstroke
Differentiator: Running through an open game reserve
Record time: 2h18m9s – Philemon Baaru (Kenya), 2014
Competitors might literally be running for their lives here as this marathon runs right through an animal-filled game reserve – and the course is patrolled by armed guards at all times.
Dubbed "Run for the Wild," its primary aim is to raise funds for conservation and community projects in Kenya, and consists of two laps of a 13-mile loop run at an average altitude of 5,500-feet.
4. Albatross Polar Circle Marathon
Location: Kangerlussuaq, Greenland
Challenge level: 8
Dangers: Frostbite, slipping into a crevasse
Differentiator: Running on a moving ice sheet
Record time: 2h57m19s – Andrew Shaw (England), 2005
This incredible marathon is run in temperatures as low as 5°F and passes by enormous glacier tongues, through tundra and across an arctic desert, as well as a 1.86-mile stretch on the ice field itself.
Runners may spot musk oxen and arctic foxes, but the biggest danger is cracks in the ice, and organisers warn against straying from the route "because of the danger of falling into a crevasse."
5. Marathon du Medoc
Location: Medoc, France
Challenge level: 4
Dangers: Intoxication, collapse
Differentiator: Marathon wine consumption
Record time: Not applicable!
Few runners aim for a time on this carnival costume marathon – it's more about fitting in the 23 wine tastings and sampling as many oyster, foie gras and cheese stops as possible before the 6h30m cut-off time.
The route runs through more than 30 vineyards, including the legendary Château Lafite Rothschild, and the event claims to have the most medical support of any marathon to cope with the consequences.
6. Burro Days World Championship Pack Burro Race
Location: Fairplay, Colorado, USA
Challenge level: 6
Dangers: Bucking, animal trampling, tripping on rocky ground
Differentiator: Off-road running with a donkey
Record time for 29-mile event: 3h44m18s – Tom Sobal and his burro Maynard (USA), 1989
There is no controlling the pace on this 29-miler, as competitors must lead, or more often be led by, a pack donkey carrying 33 pounds of mining gear in a nod to the region's Goldrush days.
The ascent over 13,123-foot Mosquito Pass is tough, but the biggest challenge is being dragged over giant rocks or through thorny bushes by burros, with organizers warning, "When one Burro runs, they're all going to run."
7. Underwater Marathon
Location: Loch Ness, Scotland
Challenge level: 7
Dangers: Drowning, hypothermia, disorientation, rock ledges
Differentiator: A full distance marathon underwater
Record time: 12 days
It took nearly two weeks for serial marathoner Lloyd Scott to do a marathon under Loch Ness wearing a 121-pound antique diving suit in this one-off event.
At one point he fell over 26 feet off a 328-foot ledge and had to be pulled up on a safety line. Afterwards, he admitted: "Visibility at times is nil, so it's very cold and very lonely – and far more difficult than doing it on land."
Scott is no stranger to epic marathons. He's run ultras in the deserts of Africa and Death Valley – and other marathons dressed as St George dragging a huge dragon, Indiana Jones being chased by a boulder and The Beatles' Yellow Submarine, raising millions for charity.
More: The world's best places to freedive