#17 RAF Menwith Hill, England

Watch your back here!
Not many people know about RAF Menwith Hill in England- probably because they do not openly advertise what exactly it is they do here.
This is strange because this unassuming site is actually known by many to be the most extensive, prominent and strongest monitoring site on the globe. It is effectively managed by both the NSA and the Royal Air Force and, due to the nature of what it does, you cannot just request a casual tour of its premises!