For most of us, our exposure to bank vaults probably doesn't extend beyond the clever bank heists we've seen in movies like "Ocean's 11" and "Heat." In reality, of course, those types of crimes are very, very rare. That's because bank vaults and other covert bunkers that hold valuable goods use some pretty amazing technology to keep things secure. In fact, these ultra-exclusive enclaves of riches have a lot of secrets. (See also: The Best and Worst Places to Stash Cash in Your Home)

Here are 10 things you probably didn't know about them.

1. They Were Invented as a Result of the Gold Rush

At least in the U.S., bank vaults as we know them today emerged during the Gold Rush of 1849, when unsuccessful prospectors gave up on finding their gold in the ground and decided to get it the easy way — by robbing a bank. At that time, banks used safes to protect their goods, and bank robbers took to heaving these out the window, hauling them off, and breaking them open in a secure location. Banks quickly decided they needed a secure solution that couldn't be carried off by a determined thief. As a result, safes got ever larger and heavier until, by the 1920s, most banks were using huge, built-in vaults, with walls and doors that were several feet thick.

2. There's a Technological Arms Race With Burglars

Of course, for every genius who can invent a lock, there's another one who can learn to pick it. That sort of technology arms race is ever-present in bank security.

Enterprising burglars have cleverly used gunpowder, nitroglycerin, and acetylene torches to pry open the tiny vulnerabilities each new bank vault provided. Today's most secure bank vaults include more technology than ever, including things like heat sensors, motion detectors, and alarms. The very most secure vaults even include things like 22-ton vault doors, machine-gun wielding guards, three foot keys, and robots. When you're guarding trillions of dollars, you can't be too careful.

3. But They've Stuck With a Clever and Innovative Type of Lock

When bank robbers learned to blast through safes with key locks, inventor Linus Yale Jr. introduced a combination lock. But it wasn't long before burglars learned to drill holes in the lock's case and peer inside at the gears to open the lock. And, of course, the simplest way to get into any lock is simply to hold the bank manager hostage until he agrees to open it. So, a man named James Sargent came up with a combination lock that wouldn't open until a set number of hours had passed. Time locks and time delay locks are still used in bank vaults as theft deterrents. Of course, for those who work at the bank, not being able to open the vault when you want or need to can occasionally prove to be most inconvenient.

4. They Are Built to Withstand *Almost* Anything

Although the latest bank vaults are built to be disassembled more easily (while still being ultra-secure), historically, bank vaults were built to last. Forever. As a result, some of them will survive almost anything. Even a nuclear blast. In fact, it was two Mosler bank vaults at the Teikoku Bank — and only those two bank vaults — that were left standing after Hiroshima was hit by an atomic bomb in 1945. In 1957, the U.S. also blasted a bank vault during nuclear testing in Nevada. The 37-kiloton nuke merely loosened the vault's trim.

5. But People Get Through Them Anyway

Most bank robbers don't even bother with the bank's vault; according to the FBI, the vast majority of crimes happen at the counter. Of course, that isn't to say that there aren't a few clever criminals who make carefully planned attempts against a bank vault's security features. Sometimes it even works.

In 2003, what was believed to be the most impenetrable diamond safe in the world, the Antwerp Diamond Vault in Belgium, was quietly opened during the night. The thieves took so much loot — $100 million worth — they couldn't even carry it all away. They set off no alarms. To this day, no one's entirely sure how they pulled it off. You can read about what's now known about the heist in this Wired piece about one of the men who was finally convicted of the crime. It's better than fiction.

6. They're Used to Hold Some Unusual and Unexpected Things

Generally, bank vaults are used to hold what we'd typically imagine as valuable goods: Cash, gold, jewels and the like. However, many of the privately owned vaults and depositories are just as impressive, although they hold some unexpected treasures.

The Granite Mountain Records Vault in Salt Lake City holds the world's largest collection of genealogical records and records of importance to the Church of Jesus Christ of Latter Day Saints.

The Pionen Bunker deep under Stockholm houses a data center that rents secure server space and bandwidth to a number of clients, most infamously WikiLeaks.

The Vatican also secures a vault of secret archives in Rome. Its labyrinthine vaults and tunnels hold all kinds of relics of Catholic history, many of which have been kept secret from the public.

There's also the Svalbard Global Seed Vault, a repository of crop seeds from the around the world.

There's even a vault just for Colonel Sanders' secret recipe. That's right, KFC's secret seasoning is hidden in a super-secure vault in Louisville, Kentucky.

7. Some Use Natural Protection

Drilling or blasting through bank vault walls has long been a concern in terms of security, which is why some of the most secure vaults are located underground — or under mountains. The Svalbard Global Seed Vault would certainly survive Armageddon in its cozy space buried 390 feet under a Nordic mountain. The Granite Mountain Records vault is under, well, Granite Mountain. And, in Germantown, New York, a former limestone mine below Iron Mountain houses historic records, a data center, and all kinds of mysterious things held by confidential tenants.

8. Some Are So Secure, No One Knows Where They're Located

There's one security feature that cutting-edge technology, armored guards, and impenetrable walls can't beat: secrecy. In Iran, the country's gold reserve remains impenetrable because no one can say for sure where it is. And that's about as much as I could find out about it.

9. Some Are So Private, No One Knows Who Owns the Goods

The Swiss are known for their banks — and their banks' secrecy. That includes top-notch bank vaults securing fortunes from people all over the world. The problem is that some of these people wish to remain so anonymous, that they won't allow their Swiss bankers to contact them. In fact, they don't leave any contact info at all. As a result, Swiss banks now hold billions of dollars of unclaimed money that goes dormant when these anonymous clients die.

10. Because They're So Hard to Destroy, They're Often Repurposed

Because many of the older bank vaults are almost impossible to destroy, they're often repurposed and incorporated into the new businesses that take over former bank buildings. You can find bank vaults, and their big, clockworks-like doors, worked into stylish hotels, restaurants, and board rooms, among other things. Well, that's one way to find yourself on the inside of a bank vault.

Have you ever seen the inside of a bank vault? How'd you get there? Share your secret in comments!