What lies within the walls of Fort Knox?
Welcome to the world's most secure vault...
Completed in 1936, it's encased in 16,000 cubic feet of granite and 4,200 cubic yards of cement.
The vault door weighs an astounding 22 tons and is made of a 21-inch-thick material that's resistant to drills, torches and explosives.
It comes with a bombproof roof, too.
Additional layers of physical security include: video cameras, minefields, barbed wire, electric fences, armed guards - even unmarked Apache helicopter gunships.
Oh, and it's stationed on a 109,000-acre U.S. army post.
So what's inside?
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