It's the centerpiece of virtually every modern UFO theory and a symbol for everything the government doesn't tell us.
About an hour's bus ride northwest of Las Vegas, Area 51 is one of the most famous military bases in the world, in part because the government barely acknowledges its existence.
According to UFO lore, Area 51, near Nevada State Route 375, otherwise known as "Extraterrestrial Highway," is where the Pentagon has, for decades, stored frozen extraterrestrials and recovered alien spacecraft. In the movie "Independence Day," it was where the heroes led a final attack against alien invaders.
But now that the CIA has started to declassify top secret programs developed at Area 51, former military officers and engineers are beginning to shed some light on the enigmatic airfield and give the UFOlogists some new information to consider.
"No one really knew we existed," said Thornton "T.D." Barnes, 72, a former special-projects engineer at Area 51. "Even our wives didn't know where we were going when we left Monday morning and came back Friday evening."
A specialist in advance radar and Soviet MiG fighter aircraft, Barnes said he was tapped by the CIA to join a "cadre" of experts that could handle any kind of military project.
As an electronics engineer for NASA, he worked on the country's first rocket plane, the X-15, the Apollo space capsule and lunar lander research vehicles.
At Area 51, he helped develop the A-12 OXCART, a super-secret spy plane built by the Lockheed Corporation. Barnes said his colleagues conducted 2,850 test flights of the A-12 out of Area 51.
Traveling 2,200 mph at 90,000 feet, nothing could catch the planes. But, he said, people would see flashes of light.
That, he thinks, is what started the rumors of an extraterrestrial safe haven.
In some ways, Barnes said, the UFO myths actually helped keep the site's true activities under wraps.
"We considered it to be a bonus," he said. "They made it easier to conceal what we were doing."
If anything, he emphasized, "We were the UFOs."
In reality, he said, compared to previous positions with frequent missions, "Area 51 was the most boring place I ever worked."
No aliens, no spacecraft from far-flung planets, no underground passageways, he said.
The only underground area he recalled was beneath a nuclear testing site at neighboring Jackass Flats.
Now that the OXCART program has been declassified, he and his colleagues are working with universities and government agencies to share their knowledge.
His program was one of the CIA's better programs, he said, but as they declassified information, they realized just how much they didn't know and couldn't share with the engineers working on similar projects today.
"They're finding that a lot that we did under secrecy, they're making the same mistakes again," Barnes said.
Harry A. Martin, 77, who supervised the fueling of the spy planes for four years, said his time at Area 51 was also one of the highlights of his career.
"I was real proud of what we accomplished," he said. "I'd never worked with a group of people who were better than those."
As for the aliens and UFOs, "people have an imagination," he said. "We laughed at it."
But some UFO experts say the former insiders' accounts don't necessarily eliminate the possibility that Area 51 is indeed home to some UFO-related activities.
"Those guys who came forward may very well be telling the truth, with the caveat that they wouldn't know if there was something going on," said Stanton T. Friedman, a nuclear physicist, lecturer and top UFO researcher.
Highly classified work is also highly compartmentalized, he said. And the absence of evidence on their part isn't the same thing as the absence of evidence for such work, he suggested.
Friedman said it's still conceivable that wreckage from what some people believe was a UFO crash in Roswell, N.M., could have been transported to Area 51. And, he added, "of course" the military has an underground base out there.
But, regardless of whether or not Area 51 is indeed connected to UFO activities, Friedman pointed out that the facility has captured the imagination of Americans for another important reason.
It has become a symbol of government secrets and the universe of information too sensitive for public consumption.
As a scientist for General Electric, Westinghouse, McDonnell Douglas and other high-tech companies, Friedman said he's worked on a variety of classified projects that have shown him government secrets are a fact of life.
Area 51 is just one example of that.
"National security has a real place in all of this stuff. There is no way to tell your friends without telling your enemies," he said. "A lot of Americans woke up to the fact that there's a lot going on that they don't get told about."
ABC News' Lee Speigel contributed to this report.