You probably can't hear most of it, but this over one-minute-long recording is proof of the world's longest echo. Set by a group of scientists inside an abandoned wartime fuel bunker, The Independent reports that it was created by firing off a pistol loaded with blanks. "I started off just playing around, whooping and hollering. The sound just goes on and on and on," Trevor Cox, the record setter, tells The Independent while describing the tunnels. "Then when we fired the pistol my initial reaction was disbelief; the reverberation times were just too long. I knew immediately we had a new world record."
Not all frequencies made it through the complete echo — reportedly totaling 112 seconds long — leading to Guinness World Records only counting 75 seconds of it toward the record for longest echo in a man-made structure. But even so, it still blows past the previous record of just 15 seconds in 1970. The Independent has more details on the record and the history of the Scottish oil storage complex, named Inchindown, where it was set. You can also head over to the Royal Commission on the Ancient and Historical Monuments of Scotland for photos inside Inchindown's labyrinthine tunnels.