The bigger the secret, the heavier the security. Both government agencies and private ones have their building complexes that need high security and here are some that are still a total mystery to most people.
Kentucky's Fort Knox Has Possibly the Best Security on the Planet
Besides the tons of gold, it used to hold the Magna Carta and even the Declaration of Independence. It is said that the walls of the facility are unbreakable, but a lot of people think that all of the security is guarding nothing and that it is all a hoax since one senator demanded an audit a couple of years ago but still hasn't gotten it.