They called it The Bloop. Back in 1997, a group of marine scientists monitoring the Pacific Ocean recorded a sound no one had ever heard before. The scientists had encountered many odd noises before, but this sound, which lasted a minute and originated somewhere 1,500 miles off the coast of Chile, was the loudest unidentified underwater sound ever recorded. It was exponentially louder than a blue whale and, according to one of the scientists present, “it didn’t seem to be manmade.”

Watch this video from the Atlantic. Prepare to get goosebumps.