There are some trails that no human would really want to hike on let alone ride a bike on. There's a completely new set of challenges that come with mountain biking down trails that are considered so dangerous that they could be fatal - and none of them should be left to chance. A bike requires extreme balance and as much as it might be an extension of the rider themselves, there's no saying whether or not a trail such as these can actually be done safely.

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Those who have done it come back with incredible footage or photos of the ascent or descent, much of which is vertigo-inducing. If it's a trail that a person wouldn't be comfortable walking on let alone biking, there's only one thing to say: no thank you... we'll stick to our local woodland trails.

Porcupine Rim Mountain Bike Trail, Utah

Moab, Utah, is actually home to several unbelievable mountain biking trails - but none that the average biker would actually want to tackle. The Porcupine Rim Mountain Bike Trail is one of several that features a death-defying cliffside along which riders must navigate without even thinking of looking down. Just over the cliffside is a rough tumble (which is putting it mildly) down to the bottom river.

However, this is also what makes it one of the most famous biking trails in the entire world. Starting at the top of the mountain, the trail descends down in switchbacks to the bottom with little to no room for error in its navigation. The trail is full of rocky terrain that must be expertly navigated lest riders lose the one to two feet they have away from the edge of the mountainside. For those who still aren't daunted, at any given point, that drop over the edge spans hundreds of feet to the bottom.

Cliffs Of Moher, Ireland

The Cliffs of Moher are an intimidating set of cliffsides, in general, and even those who walk to the edge are bound to feel, a little unsteady on their feet. Biking brings on a new type of fear - or adrenaline, depending on who you are - when it comes to this unbelievably narrow bike path. The path sits hundreds of feet over a roaring ocean which doesn't help matters and if it happens to be foggy, as it often is in Ireland, there's a sense of disorientation that can also alter a person's mindset.

With the Atlantic Ocean serving as a dark abyss below and nothing but a sheer wall above, this trail is not something to be attempted by anyone who isn't a professional. And even then, it's dicey and extremely technically challenging. With a 500-foot drop to one side, it's one that's probably better left seen from above.

Yungas Road, Bolivia

Yungas Road goes by the welcoming name of 'The Death Road' thanks to its sheer drops off the side of a mountain that already has a dizzying height. Throw in the fact that the road itself is not always in the greatest condition, landslides that are unpredictable, and additional car traffic, and you've got something that's altogether a no-go.

Despite that, bikers have tried and, tragically, 13 of them have lost their lives along this road since 1998. The misleading thing about this road is that it's flat, which has people mistaking it for being easier than many other 'dangerous' roads. While it's flat, it also features sudden and short switchbacks, a steep descent, and narrow turns that are barely big enough for the cars that try to get around them.

Annapurna Circuit, Nepal

Nepal is known for its mountain ranges and, of course, the king of all mountains: Everest. That alone should spark some fear into the hearts of those who choose to bring their bikes and tackle any range in this area - but it has been done before.

It shouldn't be said that this circuit is any less dangerous than any other, but it is more popular with bikers who wish to showcase their skill and achieve incredible heights - literally. This takes bikers through the tenth highest mountain in Nepal and various terrains, from dirt to snow, are all obstacles depending on the weather patterns and the season. Therefore, environmental hazards are also an added concern while biking this trail, as well as the elevation and potential for altitude sickness. The views from the top are breathtaking but aren't always worth the risk of being on top of one of the region's highest mountain summits.

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