5. Iron Mountain’s National Data Center, United States
Carved 220 feet underground into a former limestone mine in Pennsylvania, Iron Mountain is an elusive company operating the top secret National American Data Center. The aim of this center is to protect valuable data in the event of natural disasters and it is widely considered one of the most secured facilities of its kind. It features an underground lake used to cool data systems and a facility named Room 48 –used to discover geothermal conditions to create the perfect environment for electronic documents. The charred remains of United Flight 93 can be found here as well as some of Bill Gates’ private photographic collections.