Guardian Telephone Exchange Tunnels

Hidden deep beneath the streets of Manchester, England, the Guardian Telephone Exchange was a secret underground tunnel system built in 1954 to provide secure communications in the event of nuclear war. 

The nuclear tunnel was classified under a "D Notice"—an official request to newspapers not to publish items on subjects for reasons of national security—in the 1950s, and its existence remained a secret for over a decade, only being publicly acknowledged in 1968.

Constructed at cost of £4 million, the Exchange tunnels were built at a depth of 115 feet running for over a mile-and-a-half under the city, and are completely self-sufficient. While they are still intact today, much of the equipment has now been removed. Today, the tunnels are known to house British Telecom cables, confirmed when a fire in March 2004 caused 130,000 telephone lines in Manchester to be cut off.

While other entranceways are dotted across the city, the George Street building is the most visible part of the Exchange. Located on a quiet city back street and surrounded by barbed wire, the structure houses the facility's large goods entrance. Lifting equipment is hidden in the tower and a 35-ton cover inside the main building can be slid over the entranceway.