Transcript for The Top Secret Bunkers the Government Doesn't Want You to Know About: Part 3
Reporter: The idea of a designated survivor isn't just about a single person, but a whole way of keeping a government and a country going in the wake of a catastrophe. But the location where that would take place is beyond classified. So, consider this for your eyes only, as ABC's Pierre Thomas shares the secrets above ground and below. Reporter: It's a far cry from the polished marble and majestic buildings of Washington, D.C. Tunnels chiseled out of solid granite. Bunkers hidden deep underground. They are the shelters of last resort for a government under catastrophic assault, not just for the president, but congress, and the supreme court. Most are closely guarded secrets, but here is what we do know. From the air, you'd never guess that in the wilderness of Virginia's blue ridge mountains, there's a massive facility called mt. Weather. We have to have a way to make sure that there will be a government if Washington, D.C. Is attacked. Reporter: Andy card, white house chief of staff for president George W. Bush says, these places are the heart of continuity of government plans. So secure, they are classified beyond top secret. It's called sci, secure compartmentalized information. These are some of the best-kept secrets in government. The secrets are there for a reason. They're there to protect. Reporter: But some have become known to the public, like here in Colorado, nicknamed the mountain. Cheyenne mountain air force station is 2,000 feet deep. Hidden behind multiple 25-ton blast doors three feet thick. Five acres dug out of the rock, 15 buildings built to withstand a nuclear bomb. Supported on these 1,300 half-ton steel springs. Like a shock absorber. Reporter: There's a power plant, a 6 million gallon water supply, potentially ready to support not just the president, but hundreds of staffers to help him. ABC news consultant Richard Clarke knows. He once ran the continuity of government program. Copy, range is green. Reporter: Much of it close and dagger. The continuity of government program is always running 24 hours a day, seven days a week. Reporter: A program so secret, even the white house chief of staff was kept in the dark when he visited. They covered your eyes and your ears so you wouldn't know or have any idea where you were going. That's an accurate description. I did not know where I was being taken. And I was transferred from one vehicle to another vehicle and kind of right out of the movies. Reporter: For example, here, at the end of this corridor in West Virginia, the wallpapers panel slides away, revealing this. Welcome to the bunker. Reporter: Its one of the great U.S. Government secrets of all-time -- the greenbrie re bunker. The floor is five feet thick. The walls are five feet thick. The ceiling is five feet thick. We're in a big concrete box. Reporter: This facility was built to house congress if the U.S. Capitol was destroyed. This is the tunnel members of congress would use to enter the bunker in case of a catastrophic attack. Sealed in by a 30-ton blast door, 60,000 pounds of concrete and steel to protect. The greenbrier bunker dates back to the height of the cold war. Nuclear devastation was a clear and present danger. President Eisenhower went to the posh greenbrier resort with a You want us to do what? Reporter: He asked them to build a 112,000 square foot underground bunker beneath the hotel, and keep it secret. This was a serious matter that required novel thinking. Right. It's pretty phenomenal. It's a hell of a story. Reporter: Greenbrier historian Bob conte says it was ingenious. There was a ready made cover story, the hotel was expanding. Somebody comes up with the idea, "We'll build two buildings. We'll build an overt building and a covert building. We'll do it simultaneously." When the project began, the lakeside golf course was nine holes. By the time the project was finished, it was 18 holes. Reporter: The dirt's got to go somewhere. Where did the dirt come from? The bunker. Reporter: Three years of construction later, there were 18 dorms, a hospital clinic, a giant auditorium with exactly the number of seats for every member of the house of representatives. Even a studio for TV broadcasts. This feels kind of scary. It is scary. Reporter: All deadly serious. This is where they came to get cleaned off? These showers designed for the newly arrived congressmen to be decontaminated from nuclear fallout. Up to 240 people an hour. No time for modesty. And the clothing would have gone in, it would have been burned in an incinerator in the power plant. After the shower, there would have been someone with a Geiger counter and if you glowed, back you go. Reporter: For three decades, the bunker was in a constant state of readiness. Until one day, "A Washington post" reporter found out. When this secret came out in 1992, how angry were people? It was very troubling, and we weren't happy when it was done. Reporter: Someone described it "As awful as if a nuclear bomb had taken it out." This bunker was in a state of readiness at all times. Reporter: The greenbrier bunker forced to become a tourist attraction. And congress needed a new secret backdown H backup home. And where it exists, we don't know, but we do know the continuity of government plans were executed for the first time ever on that one tragic day. On 9/11, things did not go exactly according to plan. Most federal workers couldn't even get out of D.C. Most of them couldn't get to their alternate sites because the traffic jam on 9/11 was such that they couldn't get out of Washington. Reporter: Meantime, president bush was in Florida. I said, "Get a line open to the vice president. Get a line open to the white house situation room. Get the crew back on air force one. We're going to have to leave." Reporter: It becomes clear to you guys, you can't go right back to Washington. It became clear to me. I'm not sure it was to clear to the president. Reporter: Andy card says bush wanted to return but was convinced otherwise. It's not just going to protect the person, it's going to provide that person a venue where they can meet their spots. Reporter: Bush ended up at strategic air command in Nebraska. FBI and dhs is reporting a credible threat. Reporter: But were lessons learned after 9/11? Can we be sure things would work any better if continuity of government had to happen now? No, we can't be sure at all. These are difficult issues for people to raise and deal with and the easiest thing to do is put your head in the sand. Reporter: Norm Ornstein founded the continuity of government commission. He says, since 9/11, no significant steps have been taken to address the problems. We have no plan in place if the supreme court or congress are wiped out or designated in any significant way. It is mandatory that we have our constitutional institutions in place as quickly as possible. Incredibly alarming united States capitol building in flames. Reporter: Ornstein and many others are hoping the newfound attention from the fictional "Designated survivor" will renew focus, forcing the federal government to truly answer two critical questions, "What if?" And "Are we truly prepared?"
This transcript has been automatically generated and may not be 100% accurate.