It may also be one of the most radical.
"This is prison utopia," American prison warden James Conway said in "The Norden," a made-for-TV documentary. "I don't think you can go any more liberal - other than giving the inmates the keys." The production explored Conway's experience visting Halden.
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The 75-acre facility tries to maintain as much normalcy as possible, an important concept in the Norwegian prison system, Jan Stromnes, deputy head of the prison, said in the documentary. That means no bars on the windows, fully equipped kitchens, and friendships between guards and inmates.
"Every inmates in Norwegian prison are going back to the society," Are Hoidel, Halden's director, said in another production by Gughi Fassino and Emanuela Zuccalà. "Do you want people who are angry - or people who are rehabilitated?"
Like many prisons, Halden seeks to prepare inmates for life on the outside with vocational programs: wood-working, assembly workshops, and even a recording studio.
Norway hasn't imposed the death penalty since 1979. Life sentences don't exist, putting the focus on rehabilitation instead of punishment.
The Scandinavian country has an incarceration rate of 70 per 100,000, totaling 3,571 inmates for the entire country. The US' rate is more than 10 times Norway's - 707 per 100,000, or 2,228,424 people behind bars.