4 Grand Cayman Island -ThinkstockPhotos-97850864.jpg

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Penny Palfrey, an Australian-British swimmer, became the first person to swim 67.25 miles between Grand Cayman Island and Little Cayman in the Caribbean in 40 hours and 41 minutes. She set the world record for the longest solo unassisted ocean swim, according to World Record Academy. There are conflicting reports whether sharks were killed during the swim to protect Palfrey, but they were definitely near her. She was also stung three times by jellyfish.