12,000 years ago, in the small island nation of Palau near the Philippines, a rock on the island fell, separating a marine lake from the ocean. Jellyfish were trapped inside and managed to thrive and survive without any predators. In time, they evolved to lose their sting, as they no longer needed it to defend themselves. Nowadays,visitors to Eli Malk rock island can swim in Jellyfish Lake without suffering from any stinging injuries.
Sooo….cool!
(source)
