PHOTOS: The World's Greatest Stunts
Will Nik Wallenda add another by walking over Niagara Falls Friday?
PHOTOS: The World's Greatest Stunts
Robbie Knievel during his successful 231-foot jump over the Grand Canyon, May 20, 1999. WATCH WALLENDA'S WALK ON THE FULL EPISODE NOW (John Gurzinski/AFP/Getty Images)
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