The Bank of England's gold vault has more than 400,000 gold bars - worth roughly $257 billion. If you stacked them all on top of each other, they would be the same height as 46 Eiffel Towers.
They hardly ever let anyone in to film, but the BBC's Frank Gardner has been given access.
The vault was turned into a staff canteen during WW2. There have been no heists since the bank's establishment in 1694.
(Filmed and edited by James Wignall and Erica Brown)