How Do You Build The World's Longest Reverberation Chamber?

by accident as it happens,

excavated out of solid rock between 1939 and 1941, an oil tank was dug deep into a hillside amid concerns about the strengthening of Germany's armed forces and the threat posed by long-range bombers, the tunnels were to provide a huge bomb-proof reserve supply of furnace oil for the warships of the home fleet at Invergordon, a key Royal Navy anchorage, access to the tank is through one of the 18 inch diameter oil pipes because there are no doors, the tank was designed to hold 25.5 million liters of fuel and has walls 45 cm thick, the space is about twice the length of a football pitch, 9m wide and 13.5 meters high,

so how long does the reverberation last? (do not call it an echo), well have a guess, and then watch the video, I was out by a long shot, for the technical, have a look here, and if you want to hear something really eerie, 

listen to Trevor Cox playing his saxophone with the worlds longest reverberation.