You may be aware of Fort Knox from the James Bond movie Goldfinger, or from the old cartoon where Bugs Bunny tricks Yosemite Sam into digging up some of the gold bars and getting arrested.

But what do you really know about the U.S. bullion bunker in Kentucky?

The Fort Knox gold vault is one of the most secure and secret places in America. Because few people have ever gotten inside, the gold depository is a subject of fascination and speculation.

Here are 10 things we know — and maybe don’t know.

1. It holds tons of gold — literally

Fort Knox currently houses 147.3 million ounces of gold. The government says the bullion has a “book value” of $6.22 billion.

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However, that’s based on a fixed price that officials set in 1973. Based on the current market value of gold, the reserves at Fort Knox are worth a far more impressive $273.7 billion, roughly speaking.

Much of the gold in the vault is in the form of 27-pound bars, while a percentage is in gold coins.

At one time, the point of having all of that gold was to provide backing for U.S. currency — but the dollar was taken off the gold standard in 1971.

Read more: Moneywise