For some people, 'normality' is a dirty word. Adrenaline seekers are constantly looking to push the limits of what a human can (and should) possibly do. Whether that's swimming with sharks, climbing a mountain or just riding a particularly scary rollercoaster, there's always a boundary that needs crossing. Stunt performers, otherwise known as daredevils, have existed for many centuries across the world. Some of the earliest examples of daredevils came in the form of circus performers, such as acrobats and gymnasts. Still a popular act today, acrobats will perform daring leaps across dangerous obstacles in front of a crowd. Today, the business of daredevilry has never been better. Hollywood still calls for stuntmen to perform terrifying feats on film, while companies such as Red Bull have specialised in sponsoring the more extreme daredevils as they race or compete for world records. There is a darker side to the romantic idea of a daredevil. With the rise of sharing videos and photos online, there's been a growing trend of youngsters placing themselves in precarious situations in order to get a remarkable shot. This has gone on to create a number of YouTube celebrities, but there have been more than a few fatal incidents associated with the dangerous activity. This article takes a look at 15 absolutely terrifying photos, of and by the world's biggest daredevils. From stomach-churning urban heights to ridiculously dangerous races, at least one of your phobias is sure to be triggered somewhere here...