Photos: Inside Cheyenne Mountain, America's Fortress

A thousand feet up a restricted-access road from Colorado Springs, Colo., is Cheyenne Mountain. Long thought of interchangeably with NORAD, the North American Aerospace Defense Command, Cheyenne Mountain actually houses elements of NORAD, as well as many other U.S. government defense-related agencies, including Air Force Space Command, U.S. Strategic Command, the National Security Agency and more.

Situated under 2,000 feet of rubble, Cheyenne Mountain--which, contrary to popular belief, is still fully functional--was designed to house critical government and defense functions in case of a nuclear strike. To this day, its infrastructure is meant to protect the interior of the installation against just about any kind of attack.

This is the famous tunnel that leads into Cheyenne Mountain.

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Fans of the film "War Games" may remember the huge Cheyenne Mountain blast doors. They're still there, and still fully functional. The doors are designed to protect the interior of Cheyenne Mountain against almost any kind of attack, including nuclear, biological, electromagnetic pulse, and others.

Each door weighs 25 tons, yet is meant to be pushed closed by as few as two people if necessary.

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Cheyenne Mountain's main entry--already deep inside the mountain--has two blast doors like this. It's easy to see, from the thickness of the doors, that the installation was meant as a fortress against enemy attack.

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A wide view of Cheyenne Mountain and the famous tunnel that leads to the military installation, which is secured under 2,000 feet of granite.

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The formal entryway into the Cheyenne Mountain facility features the insignia of four of the installation's tenants: NORAD, U.S. Northern Command, Air Force Space Command, and U.S. Strategic Command.

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There are actually several buildings inside Cheyenne Mountain, each fully three stories high. Here, you can see the height of the main building inside the main cave entry.

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Anyone entering the Cheyenne Mountain complex must go through this security checkpoint. Despite the sign prohibiting photography, CNET News reporter Daniel Terdiman had authorization to have a camera with him.

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Upon entry into the Cheyenne Mountain complex, visitors and employees are faced with a choice: Which adit, or underground entrance, do they take? The complex features three adits.

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In the highly unlikely case of a complete emergency in which none of the other exits are available, those inside the Cheyenne Mountain complex can leave via this tiny trap door, which offers a crawlspace out of the facility.

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One of the many Cheyenne Mountain features designed to protect the complex from a nuclear blast--or an earthquake--are these giant springs.

Placed under the complex's buildings, the more than 1,300 1,000-pound springs are meant to allow the structures to shift up to one full inch in any direction. Combined with a set of dampers, the springs are expected to protect the building, their contents and the people inside them.

These springs are pushed down significantly by the weight of the building. But from time to time, the springs must be adjusted to account for changes in the weight of the building and its contents.

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Blast valves like this one are installed at the Cheyenne Mountain complex to protect the air that those inside breathe. They feature filters that can cleanse the air coming in.

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Inside the Cheyenne Mountain complex, it's nearly impossible to tell when you're moving from one of the several buildings to another. But here, it is possible to see through this special window that there is separation between two buildings and that they are wedged into the granite of the mountain. In most places where there's separation, the only indication is the appearance of the gray material that surrounds this window.

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Like the giant springs found throughout the Cheyenne Mountain complex, there are many of these flexing connectors between various piping. The idea, like with the springs, is to help the complex's infrastructure--in this case, the many pipes inside--to survive a major blast.

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While Cheyenne Mountain now has commercial Colorado Springs power as its primary source of electricity, it used to rely entirely on generators.

Now, the generators serve as backups in case of a loss of the city electric power. The complex features six generators, four of which can run normal operations inside the mountain. Only two, however, are needed for the most mission-critical operations. Two more generators are available in case one is under maintenance, and another is a spare.

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The front of one of Cheyenne Mountain's six generators.

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The rear of one of Cheyenne Mountain's six generators.

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This sign illustrates the sentiment that air conditioning is vital to the operations inside Cheyenne Mountain.

Contrary to popular perception, there are no furnaces or other heating infrastructure inside the mountain. Rather, it features four giant chillers designed to help cool the interior. Only two are needed at any time, so two are redundant.

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Deep inside the complex is a reservoir of diesel fuel that has a capacity of 510,000 gallons, though it is not filled all the way. The fuel is floated on several feet of water in order to keep it from seeping through the granite.

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The process of shutting down access to Cheyenne Mountain in the case of an attack or a drill is called "button up." This shed is one of many throughout the complex that are full of equipment that might be needed in case of such an event.

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If Cheyenne Mountain is in "button up," the complex needs a giant heat sink to maintain a cool interior temperature.

For that purpose, the complex has a reservoir with a capacity of 4.5 million gallons of water. This is one "leg" of the reservoir, which is spread out in the shape of an E.

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To many people, this "duck" on the surface of the reservoir is the most famous element inside Cheyenne Mountain. Reportedly, it was placed there by maintenance divers who wanted a way to orient themselves while underwater.

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The main Cheyenne Mountain entrance is in the center of the facility. But there are also two lesser-known portals, one to the north, and another to the south. Among other things, the south portal is where fuel is brought in so that gravity will push it downhill into the main part of the complex more efficiently than having it pumped up from the north portal.

This tunnel heads toward the southern portal.

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A view out, and toward the light, of the main tunnel that heads into Cheyenne Mountain.

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