"On June 17, 1908, Houdini, heavily manacled, dove off Young’s Pier at Atlantic City, New Jersey, before a crowd of more than twenty thousand. He usually jumped feetfirst into waters that he was unfamiliar with, but on this day, he decided to dive, despite being warned against that by the lifeguards. He knifed through the water perfectly but then struck his head on the bottom of the ocean floor. Dazed and bleeding, he somehow managed to remove his handcuffs."
Curiously, Houdini appears to have been on vacation in Atlantic City this week, so it's unclear why he would be doing an outdoor stunt in the first place [see update]. Unless it was to impress his mother, who was vacationing with him, or Harry Kellar, who had recently retired to Atlantic City. The below photo of Houdini and Kellar was taken by Franz Kukol three days after the jump. Houdini doesn't appear to be any worse for wear from his mishap.
This is an updated post that first appeared on Sept. 25, 2016.
UPDATE: Correction. Houdini was not on vacation this week. He was playing the first of two weeks at Young's Pier Theatre. Thanks to Bill Mullins for this info.