Scientists have broken the record for the world's longest man-made echo.
The record was smashed deep inside a giant oil storage tank, constructed during World War 2 underneath Rossshire in Scotland.
The tunnels were excavated in 1939-41, built to keep a reserve supply of furnace oil safe from German bombers. The tank itself was able to hold 25.5 million litres of fuel, and has 45cm-thick walls.
'Acoustic scientists' were able to prove that a gunshot inside the tank resonates for a full 75 seconds - much longer than the previous record, which was also achieved in Scotland.
The old record was, well, recorded at the Hamilton Mausoleum, where the sound of a door slamming was found to last at least 15 seconds back in 1970.
But to break the record, Trevor Cox, Professor of Acoustic Engineering at the University of Salford, had to look for somewhere a little more isolated. When he found the Inchindown fuel tank, and gained access via an 18-inch diameter oil pipe, he knew he had something special.
Cox then stood by as Allan Kilpatrick from the Royal Commission on the Ancient and Historical Monuments of Scotland fired a pistol loaded with blanks from a third of the way inside the two-football pitch-sized tank.
The shot itself was recorded and can be heard below:
The Guinness World Records organisation certified the findings, recording that the "broadband reverberation time" lasted for 75 seconds.
"It was like going underground into a Bond villain's lair. But never before had I heard such a rush of echoes and reverberation," Prof Cox told the Independent.
"I started off just playing around, whooping and hollering. The sound just goes on and on and on.
"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."