A fifth of the world's gold is hidden under London, worth an estimated £172 billion ($248 billion).
The vaults under the Bank of England on Threadneedle Street are said to hold 5,134 tonnes of gold.
This makes up the majority of the 6,256 tonnes kept safe beneath London's streets, according to the BBC, which recently sent a reporter to visit the 300,000 square foot space.
Gold is measured in bars weighing precisely 400 troy ounces, or 12kg, worth around £250,000 ($500,000). Gold is used by investors as a safe asset to invest in when the stock market and other assets are more volatile, because it is so low risk.
The price of gold can thus be used a barometer for the confidence of investors. When it goes up, investors are looking to invest in gold because they may be worrying about higher risk assets.
It can also be traded and used as a way to exchange funds in a hard and universal currency.
While Britain doesn't own as much gold as other countries, it does guard one-fifth of global stock. Partly because it has a system called the London Good Delivery which sets a standard for large bars, making them easier to trade.
Nonetheless, the shape of the bars the BBC sees in the vault varies. Some look like loaves of bread while others have slanted edges to allow them to be picked up more easily. They are kept rows of blue numbered shelves in the silence of the concrete-encased underground safe, the BBC said.
If keeping your wealth in a metal stored in an underground safe sounds like something straight out of history, or even fantasy, hold tight. The vaults, which were built in the 1930s, are still accessed using several 3ft long keys.
Security experts think the analogue measure is safer than electronic access alone, but there are electronic safeguards too. Visitors have to speak a password into a microphone that matches voices to a select few saved samples.
The vaults have their own rich history too, the BBC reports. When Britain's gold bars were moved to Canada during World War II, one vault became a staff canteen. Cruise posters still line the walls. It was later used as a bomb shelter.
The vast size of the vaults can partly be accounted for by the clay bedrock they are built on. Because clay is soft and gold can be heavy, the bars are only stacked four pallets high in the top level vaults and six pallets high in the bottom level. Otherwise they would sink into the ground.
Last year, the Royal Mint put gold bars on sale for the first time. Measuring 53mm by 118mm and 8mm thick, the Royal Mint-branded bars were put on sale at around £24,000 to £25,000, depending on the price of gold.