In the background of Colorado Springs, Pikes Peak dominates the sky. But just to that mountain’s southeast looms another geological ripple. Cheyenne Mountain—a rounded, rocky thing that rises 9,565 feet above sea level—looks wild and quiet. But deep inside the mountain, a crew of humans toils in one of the nation’s most secure military installations. Shielded by 2,500 feet of granite, these people gather and analyze data from a global surveillance system, in an attempt to (among other, undisclosed things) warn the government’s highest officials of launches and missile threats to North America.

Their military mole-city, completed in the mid-1960s amid Cold War worries, is—when fully buttoned-up—highly resistant to nuclear bombs, electromagnetic bombs, electromagnetically destructive behavior from the sun, and biological weapons. It’s designed to do its job, and let those inside do theirs, in the worst of worst-case scenarios. And with escalating fears about North Korean aggression and nuclear capabilities, Cheyenne Mountain’s ability to predict and survive a nuclear attack resonates more than it did just a few months ago.

As I drive up the hairpinned road toward the entrance to the mountain, made famous in fictional form by War Games and Stargate, signs warn me off with increasing aggression. But I'm allowed: I'm here for a rare tour of the mountain’s innards.

When I arrive at the visitor check-in, Fox News plays on the overhead TV. A sign beneath says not to change the channel, and a uniformed officer reads me a document that says I can't have explosives and that the employees can use deadly force to protect the site. Fair enough.

Soon, badge on blazer, fully briefed, I walk with four escorts—two men who are civilians and two women who are military officers—toward this constructed cave. It is, perhaps, the place on this planet most able to cut itself off from the rest of Earth. And the hardest part for those who work there is not spending all their time subterranean but knowing that in those worst cases—of which "North Korean nukes" is the example most used during my visit—everyone they care about will be outside the thing that’s keeping them safe.

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A Skyless Safety Net

Much of that safety comes from the complex’s very underground-ness. And given that miners had to excavate 693,000 tons of granite to make the Cheyenne Mountain Complex, you might expect its entryway to wow. But the mountain itself is so tall, so sheer, that the 22-foot, two-lane arch leading to the north tunnel looks especially puny by comparison.

Rusty Mullins—deputy director of the Air Force’s 721st Communications Squadron—is leading this tour. He walks down the edge of the tunnel’s asphalt road as he talks about the site, concrete barriers forcing him at intervals to step back onto the sidewalk. The granite makes a half-cylinder around us, bolts knocked into the rock like some kind of sadistic climbing gym.

People get used to these depths, the disconnection. “You learn to live without any sky,” he says, “without any outside but what’s on TV.” There's a lot of TV, though—sets in the work rooms that show the world beyond that arch.

The tunnel curves ahead of us, a skew that will route nuclear (or whatever) material and send it out through the south entrance. The blast doors that lead to the complex's buildings branch off from the tunnel at around 90 degrees, so any material will glance off rather than slam into them.

We pass through one open 25-ton door—it'll get closed in the event of a potential or impending threat to the area—and enter a rock-walled room with a second such door at its far end. A slight breeze blows by. It's coming from deeper in the mountain, the result of a purposeful over-pressurization so radioactive or bio-particles won’t seep inside the complex. They’d have to make that perpendicular turn and then swim upstream. And they won’t. That’s physics.

Back when humans were cold warring, one of these doors stayed closed. When both get shut, their uber-deadbolts and substantial concreteness keep everything out. Today, these main blast doors remain open unless something truly terrible and threatening happens (like 9/11, the last time the gates shut for serious) or the employees do a drill: what they call a button-up scenario, a practice as much human as mechanical.

Because it’s not enough for the mountain’s welded-metal buildings to sit on springs that can take a nuclear or earthquake hit, which they do, or for its pipes to be bendy, which they are. It’s not enough for the managers to know they have 6 million gallons of water stored in pools carved right out of the rock, or 510,000 gallons of diesel. They have to know the humans can do their jobs—best of times, worst of times, regardless of how sad or scared they are. And the electronics that let them do those jobs have to continue functioning, even as they're cut off from an outside that, in a real emergency, might not have working electronics.

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Sleepover

Mullins points inside the second door. Everyone’s “button-up bags” (essentially sleepover kits) are already inside. Locked in, people share bunked cots. They eat MREs—meals ready to eat, whose calorie-dense contents are almost as indestructible as the complex itself. They breathe filtered air that comes in through blast valves. Their lives run on six generators, an internal 10.5-megawatt power plant (nearby, there’s a giant door that says, “Without power, it’s just a cave.”). Any supplies they need come from cabinets and cages that they call “Wal-Marts,” where they’ve stashed extra fan belts and connectors and whatever else.

Mullins leads us through that second blast door, where an awning like those fronting old apartments juts from the first of 15 buildings. “WELCOME TO CHEYENNE MOUNTAIN COMPLEX,” it says. When the employees enter this building during a button-up—real or contrived—they can’t go back out. And no one can come in.

Inside, we cross little walkways that can move independently of the buildings. These structures don't sit together in some giant cavern: They're encased in a series of tunnels. The trim color changes from building to building, so you know where(ish) you are. As we walk, we pass a regular medical clinic, a dentist, a self-checkout store, and also the world’s most secure Subway. (One assumes that in the event of a long-term lockdown, the inhabitants would not be eating so fresh.) Down one hallway is Norad’s alternate command center, where they’ll go if shit slams into fans. We do not go inside.

Mullins leads us through staircases and hallways into a gym set up for spin class. On a normal day, an instructor might be yelling about cadence over some jacked-up pop song. But if there’s a bombing or an earthquake, this exercise room morphs into a hospital. The curtains at the front, which I hadn't noticed at first, would close over medical bays. The area would fill with bleeding people clutching broken arms and medical responders to treat them—as fast as possible, so they could get back to work. “Because you have a job on the mountain,” says Mullins.

“I’m gonna depress you,” Mullins had said before we even went inside the mountain. He described his family—wife, kids. And how for his whole career here, he’s had to tell them that if there’s some kind of Event, they’re on their own. “I’m going to be in the mountain doing my job,” he says to the people he loves most, “and I can’t help you.”

That’s a big reason Cheyenne needs run-downs. People have to practice leaving their families, friends, and favorite Starbucks locations, imagining that everyone could burn up in a nuclear blast, be left in an apocalyptic electromagnetic pulse scenario, or become bio-weapon infected.

They usually hold it together. On 9/11, just a few of the hundreds locked inside wanted to go home. One was distraught enough that officials took him to the chapel so he could sit, think, calm down. The chapel—which comes with a chaplain, whose support is bolstered by mental health services—is bland, non-denominational. It’s the kind of quiet that makes your ears ring. After 10 or 15 minutes, the guy came out. He went back to work.

They all do. “No matter how bad it is outside, I’m going to do my job here," Mullins says. He says it like a mantra.

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Closing off the Cave

That work all these people need to get back to—it involves computers. And their physiological aliveness wouldn't do much good if the computers were dead or cyber-compromised, would it? That's why the complex's shielding, both physical and digital, matters so much.

If an electromagnetic pulse hit near the mountain, it could knock out everything around Colorado Springs. But inside the complex, computers and the lines feeding into them stay safe. The rock sheath attenuates the electromagnetic waves, as do the metal buildings: They're giant Faraday cages.

Mullins leads us to a room where that protection matters a lot: the Global Strategic Warning/Space Surveillance Systems Center. Inside, the occupants have kindly put up simulated surveillance screens so I can't see what's actually going on with the world. A gray-haired civilian is in charge of smiley young staff sergeants. They're all standing in front of a herd of monitors, bluelit by a wall of screens showing (fake) maps, (fake) aircraft, (fake) bar graphs. It's exactly what you'd imagine would be inside a place like Cheyenne Mountain if you were going to make a movie about it, which people have.

Down here, they spend their time watching the skies they can’t actually see for evidence of missiles, suspicious space behavior, launches, tests—is that heat signature from North Korea a threat, or nah? They ingest information and determine what’s going on that’s good, bad, neutral, what should go up the chain to the decisionmakers. And it's here that they decide when it's time to shut Cheyenne's doors.

As we make our way back toward those (still open) doors, after three or so hours playing cavepeople, I ask how they isolate themselves digitally. If their whole operation relies on data from beyond the mountain’s mouth, how can they be so sure nothing else can get in?

We're outside the buildings now, in one of the rooms that just has granite for walls. Well, Mullins says, some of their systems don’t connect to outside networks, ever. That’s failsafe. For the rest, he turns to one of the uniformed personnel with us—Major Mica Myers, who’s been pretty quiet, cutting in to add details here and there to Mullins's narration. But I've felt the whole time like she was watching over this excursion. Turns out, I might not be wrong.

“I’m gonna use the 'DCO' word,” Mullins says. “OK, you think?”

She agrees.

“Defensive cyber operations,” he says. He points to Myers and says she, director of operations for the 721st Communications Squadron, leads them.

While they won’t say what, exactly, “defensive cyber operations” means for Cheyenne Mountain, the Joint Force Commander’s Guide to Cyberspace Operations gives a general definition: They “provide the ability to discover, detect, analyze, and mitigate threats, to include insider threats.” Basically, they identify and freeze attempts to infiltrate their cyber systems. Mullins and Myers say they have plans for various scenarios, and proof that the plans work. Proof, they repeat. And although they don't say what this means, it seems safe to assume they have repelled infiltrators either real or simulated.

Mullins looks around at the rocky walls that surround us as we turn back toward the tunnel, toward the outside world.

“We’re having a defensive cyber conversation in the middle of a cave,” he says. He laughs. That is, though, kind of Cheyenne Mountain’s whole thing: Protecting high-tech stuff with the planet itself, a womb around solid civil and anti-hack engineering.

Mullins steps back out into the tunnel. “Does it look any different going this direction?” he asks.

I can see actual light at the end of this actual tunnel, so yes.

When we step through the arch, the world is different from the way we left it. It has, as it always will (for better or worse or worst), gone on without us. The air feels colder, even though it’s noon now. Charcoal clouds hover over the eastern plains. There’s a beat of thunder. A fleet of military sirens goes off 1,000 feet below, back in town. This is just a test, they tell me.