A network of oil storage tanks hidden in the hills of Scotland during World War II is officially the most echo-friendly man-made structure on Earth—and it's not close. The report from a blank fired into the tanks reverberated for a stunning 112 seconds, the Independent reports. The previous world record was 15 seconds. "My initial reaction was disbelief," says acoustic engineering professor Trevor Cox. "The reverberation times were just too long. I knew immediately we had a world record."
Cox saw the site on TV, and had to investigate. "There are no doors, so I had to be pushed in through the 18-inch diameter pipe," which was covered in oil, he explains. "It was like going underground into a Bond villain's lair. But never before had I heard such a rush of echoes." The BBC has images of the site, which was decommissioned after the Falklands War. The previous record was also set in Scotland, at the Hamilton Mausoleum in Lanarkshire in the 1970s. (Read more echo stories.)