4. The Greenbrier Bunker, United States
The Greenbrier is a historic resort in West Virginia that frequently hosts presidents and government officials due to its relative proximity to the White House. In the late 1950s, the U.S. government approached the property to help them create a top secret emergency relocation in the event of a nuclear holocaust. The bunker was named “Project Greek Island” and was kept stocked with supplies for 30 years until a journalist in the Washington Post revealed its location in 1992 – at which point its purpose was nulled. Today, the bunker is open as an attraction to visitors and is used as a data storage facility.