They are among the most secure places on earth -- hard to get into, and nearly impossible to get out of.
They're called supermax prisons. There are 31 of them around the country, and one of the biggest is the ADX supermax prison in Florence, Colo. It's the only federal supermax in the country; the others are state prisons.
The ADX Florence prison is home to about 500 of the most dangerous criminals in the country. Almost all inmates have been transferred from other facilities, where they were deemed a serious lethal threat or a high-escape risk.
But unlike most American prisons -- relegated to the darkest or least populated edges of town -- this supermax sits in picturesque Florence, with a population of just 3,800, in the shadow of the Rocky Mountains.
The paradox isn't lost on Florence Mayor Cindy Cox, a breezy woman with an infectious laugh who boasts of the antique-hunting opportunities in Florence and the indelible American charms of a town where people still leave their doors unlocked at night.
There is no fear whatsoever," she told ABC News. "There has never been an incident. You talk to people, and they don't even know Supermax is up there. It's the American criminal capital of the world," Cox said.
She said that the only time the prison even comes up in local conversation is when they feature employees of the month in the paper. "And a lot of families follow their inmate family members around. There will be some issues in the school because some of the kids come from gang families."
No one has ever escaped from the prison since it was built in 1994.
Deep in the recesses of the Florence facility, inmates tick away the hours in solitude, with little sunlight, spending 22-plus hours a day in their cells and no access to the bucolic world just outside the prison walls.
The prison is home to a who's who of criminals. "Unabomber" Ted Kaczynski and "Shoe Bomber" Richard Reid.
Ramzi Yousef, who plotted the 1993 World Trade Center attack lives there, behind the miles of barbed wire and steel in a tiny cell deep inside the flagship facility.
Supermax prisons, with their notorious isolation wards are not without detractors. Critics call them inhumane. Several states have been sued, most often citing the Eight Amendment ban on "cruel and unusual punishment." In 2005, supermax inmates in Ohio won a U.S. Supreme Court case, using the 14th Amendment's right to "due process." The court ruled that isolation constitutes an atypical hardship and agreed that inmates have the right to appeal before prison officials can place an inmate in isolation.
Olympic Park bomber Eric Rudolph is another Florence supermax inmate.
In 2006, Rudolph wrote to a letter to a newspaper saying that being confined to isolation was driving him insane. "It is a closed-off world designed to isolate inmates from social and environmental stimuli, with the ultimate purpose of causing mental illness and chronic physical conditions such as diabetes, heart disease and arthritis, he told The Gazette of Colorado Springs.
Some supermax inmates seemed to be able to adjust to life in isolation.
Charles Harrelson, was sent to ADX Florence. The late father of actor Woody Harrelson was convicted of killing a federal judge in Texas in 1979. A troublemaker in the prison system, Harrelson got himself transferred to Florence after a failed attempt to escape from a Georgia prison.
Harrelson revealed slices of life in Supermax in conversations and in a series of letters to attorney Robert Tiernan.
"We struck up a friendship," Tiernan told ABC News. Eventually Harrelson came to describe his life inside.
"I promised to describe my cage and daily routine for you Bob. The cell is some 10' wide and 15' deep, 10' by 12' is the usable space. And then the bed, shower and commode/sink take up most of that," Harrelson wrote, noting that the one bit of the outside he saw was a slice of the sky.
"Part of the plan here is sensory deprivation," Harrelson wrote, his penmanship consistent and precise, Tiernan said.
Tiernan, who fondly recalls Harrelson as a "fascinating person, not very educated but very very smart, a real gentleman," noted that Harrelson was once deemed "a huge escape risk."
Not at supermax though, where Harrelson was something of an ideal inmate, gaining privileges such as a TV and radio over time. As a "tenant of this hospice," as Harrelson put it, he seemed resigned to the fact that there was no way out.
"I'm unable to exercise any control over anything outside this cage," Harrelson wrote. "I simply do my best with what I have."
Harrelson wrote that he generally ignored his opportunity to go outside for an hour and enjoyed the simple pleasures of a shower and reading "until the wee hours."
"The station that airs NPR in Colorado Springs switches over to the BBC radio broadcast each morning," he wrote. "It's my window on the world. I love it."
Tiernan, who visited Harrelson on a few occasions, noted a strange feeling in the contrast between Florence and the world his inmate friend called home.
As a visitor, Tiernan was led two stories down to a windowless room where he would wait, once for several hours, to see Harrelson. Tiernan characterized the experience as like being in a backward "Bizarro" world.
"The doors on the bathrooms lock on the outside instead of in. There is just no way out," Harrelson said. "And they go inside a pit, like an empty swimming pool, to exercise, so that you don't know where you are."
Harrelson, as a "cooperative" inmate, enjoyed his earned privileges inside, such as the ability to watch some television alone in his cell.
"I watch David Letterman's monologue. My other TV watching is nearly all CNN and/or PBS." He wrote that he liked "Nova," "Frontline" and "Nature," explaining to his pen pal and friend that life was bearable.
Tiernan noted that Harrelson managed to cope in Florence by taking pleasures as they came. "He enjoyed people coming to visit," Tiernan said.
"It could be infinitely worse," Harrelson told Tiernan."I could have been raised in one of those religious families. I could have been born in Darfur or Baghdad or Jerusalem or somewhere in another of those Third World countries where every bite of beans is a struggle," Harrelson wrote. "Hell, I could have been a Republican (shudder)! Those are only a few of the fates for worse than this one."
Harrelson died March 15, 2007, of heart failure. He was inside his cell at the time, of course.