Travelling the world introduces you to new sights and experiences -- after a while, though, there's only so many times you can visit the Eiffel Tower or the Great Wall of China. Eventually, you'll begin to seek out stranger and more unusual holiday destinations. Here are some of the most extreme -- and in some cases dangerous -- places you might visit.
Iguazu Cataracts, Brazil
Whitewater boating takes on a whole new meaning on the Iguazu Cataracts, a series of rapids and waterfalls that stretch between Argentina and Brazil. The wild river is thrilling, but it can be dangerous: two tourists were killed in this region in 2011.
Related: The 20 Best Brazilian beaches
CN Tower, Toronto
Toronto's tallest tower, the CN tower is one of the city's most famous landmarks. Visitors can take part in the breath-taking Edgewalk, a hands-free walk around the tower's circular platform, over 350 metres above ground level. Walkers are attached to the tower by a safety harness, but looking out over the Toronto skyline it's easy to forget that fact.
Diving with sharks, South Africa
Those who like their danger a little more face-to-face can descend into the waters off the South African coast to come close to a Great White shark. Although divers are protected from the deadly predators by a metal cage, the thrill is still completely real.
Or with crocodiles in Australia
If sharks are too old-fashioned for you, you could try interacting with another deadly predator -- Australia's saltwater crocodile. "Salties," which can grow to huge lengths, are among the most dangerous animals in a continent with no shortage. Tourists can descend into the water in a clear plastic cage to witness these fearsome animals up close.
Zorbing in New Zealand
New Zealand's steep slopes are the perfect environment for "zorbing," in which hapless tourists are placed inside a large inflatable ball and then given a shove to send them tumbling downhill. The result is a unique thrill ride that's always just on the verge of turning into a head-over-heels spin.
Even those who like a little danger in their tourism usually stay away from actual fighting -- but not all! In 2013, British journalists in Syria reported encountering a lone Japanese tourist wandering through an area of heavy fighting. He told journalists that he expected snipers to ignore him because he was a tourist.
America's Death Valley National Park is the lowest and driest part of the country; this deadly desert in eastern California is also one of the hottest places in North America, with recorded temperatures of over 55 degrees C. Best of all, after baking in the scorching heat for a while, it's only a short drive to nearby Las Vegas.
West Virginia Roadkill Cook-off
Just as food tourism has grown in importance over the last decade, so extreme foodies are now beginning to look further afield for their culinary thrills. The most dubious and unsavoury of these is the West Virginia Roadkill Cook-off, which takes place every year in the tiny town of Marlinton, West Virginia. Chefs compete to make the finest dishes out of animals killed by cars. It's all perfectly sustainable, and yet somehow still repulsive.
Ukraine's Chernobyl nuclear power plant was the site of one of history's greatest environmental catastrophes, but it's also become the one of the region's major tourist attractions. You can visit Chernobyl as part of an official guided tour, assuming that you're the kind of person who enjoys grim reminders of mankind's irresponsibility with power. Just don't stay too long.
Iraq is one of the world's richest countries, archaeologically speaking, with artefacts dating back to the earliest human civilisations. Sites such as the ruins of the Persian city of Ctesiphon would attract visitors from all over the world -- if most people weren't worried about security. As it is, only a handful of tour operators run trips to Iraq, and getting insurance can be a challenge.
The Danakil desert in southern Ethiopia is one of the most extreme holiday destinations in the world. Extremely hot, home to active volcanoes, and located along the often-contested border with Eritrea, this region has striking scenery but is only for the boldest travellers.
Orbital tourism isn't here -- yet. But Virgin Galactic has announced a deal with America's Federal Aviation Administration that could allow it to start offering tourist space flights as early as the end of 2014. Commercial spaceflight could open up a new (if expensive) way for adventure tourists to go somewhere even more exotic.