(Photo: Bullion Vault/CC BY-ND 2.0)

Around one-fifth of all the gold held by governments is beneath the streets of London, in hidden vaults that have been storing the gold in bars for decades. 

The vaults are not a secret so much as a government institution, reports the BBC. Home to the Bank of England’s gold since the 1930s, they now store nearly nearly 5,659 tons of it, mostly in gold bars, worth $200 billion; over 1,200 more tons are stored around the city of London, adding $48 billion more to the tally. 

Each bar weighs around 27 pounds, and is stacked in rows in the vault. However, London is built on clay, and if the stacks are too heavy, according to the BBC, the vaults will sink deeper into the earth. 

The gold is not all the U.K,’s; some of it belongs to other governments, or is privately owned. Accessing the vault is surprisingly old-fashioned, with metal keys. This is thought to be safer than electronic locks, mainly because metal keys can’t be hacked. 

The gold gets there through traditional means as well: by sea, or by commercial jet.

“In the cargo hold of commercial passenger planes, you often find gold, fresh flowers, and dead bodies,” Ruth Crowell, chief executive of the London Bullion Market Association, tells the BBC. 

You can’t visit the gold, of course. But if you want to get close, stand in front of the Bank of England on Threadneedle Street in downtown London, look down, and imagine.