Colorado facility where extradited terror suspects would be held is one of the most secure environments in the world

If the final extradition hurdles are cleared and the terror suspects facing extradition are made to board a prison jet bound for ADX Florence in Colorado, they should use the nine-hour flight to prepare for entry into one of the most secure, alienating and isolated environments in the world.

The supermax prison is known as the Alcatraz of the Rockies, in reference to its location tucked into the mountain range about 100 miles south of Denver. A "clean version of hell" is another description.

The prison was built in 1994 at a time of rising panic in the US prison service after a spate of breakouts and guard killings.

With that in mind, it was designed as a place from which no one would ever escape, and where institutional control was virtually total.

The 7ft by 12ft cells that Babar Ahmad, Syed Talha Ahsan, Adel Abdel Bary and Khaled al-Fawwaz would occupy – Abu Hamza would not be held in a supermax facility because of his disabilities – is like a modernist nightmare. The walls and ceiling of the cell and all its contents – bed, shower, toilet – are made entirely of poured concrete. Food would be handed to them through a slot in the steel door.

There is a small window allowing prisoners to look up at the sky – it is angled to prevent having any sense of the surroundings. When allowed out for exercise, having been in the cell for 23 hours a day, prisoners go to a concrete tub with no views by which to get their bearings.

"Florence is the most secure prison in the country and it practises extreme isolation as the norm," said Marc Mauer, director of the Sentencing Project, a prison reform campaign group. "There are extreme limits to access to other prisoners and the outside world." The men would have no contact with their 430 fellow inmates, who include some of the most notorious names in the prison system.

Among them are Richard Reid, the shoe bomber; Ahmed Ghailani, sentenced to life for involvement in the east African embassy bombings; Zacarias Moussaoui, who helped plan the 9/11 attacks; and Ramzi Yousef, mastermind of the 1993 attack on the World Trade Centre.

Other inmates include the Unabomber, Theodore Kaczynski, and the Oklahoma City bomber, Terry Nichols.

Shain Duka, convicted of a terrorist plot to attack a US army base, recently described his time inside the ADX to the Guardian. "These are places to silence us. To keep you controlled. I consider the supermax as a psychological torture chamber. That's what it is," he said.

Prison reformers have long objected to the prolonged use of solitary confinement at the ADX, which in some cases has lasted for more than a decade. David Fathi, director of the American Civil Liberties Union's national prison project, described the conditions as "extraordinarily harsh".

"Solitary confinement, even for a few months, let alone for more than a decade, can be shattering," he said.