Norway has put on show what it calls "the world's first ecological prison", where inmates play important roles in daily operations and learn to do their bit to protect the environment.
The Bastoey Island low security prison uses solar panels for energy, produces most of its own food, recycles everything it can and tries to reduce its carbon footprint.
Justice Minister Knut Storberget said the most important idea behind the "ecologically driven prison" is to develop a sense of responsibility in inmates and prepare them for life outside its non-existent walls.
Norway's relaxed prison policy is intended to reduce re-offending by released offenders, and Bastoey prison aims to bring new values to the handling of criminals.
"On a long-term basis, from a social and economic perspective, this is cheapest for society," Storberget said during a visit to Bastoey island, 75km (46 miles) south of Oslo, whose prison has a total of 115 inmates.
"Bastoey is the island of hope," he told visitors, inmates and employees in a packed church on the prison's property, which sprawls over much of the island in the beautiful Oslo fjord.
The prison gained international media attention a few years ago for its living conditions, resembling a summer camp with activities like tennis, horse riding, and even swimming in the summer, when the North Sea waters warm up.
Assistant prison manager Per Eirik Lund said running costs were lower at Bastoey than at more traditional prisons.
"On a normal day, we have five prison officers at work. In a closed facility, you have two or three officers per 20 inmates, so this is among the cheapest prison facilities in Norway."
Lund said Bastoey tapped grants from environmental bodies to help it produce high-quality food. "Most of the food is used in the kitchen here, but we also sell to other prisons or elsewhere," he said.
Surrounded by beaches and green fields, the prison grounds extend into a nature reserve and are popular with the inmates.
"We are given full freedom within a limited area," Erik, an inmate and hobby carpenter who helped install solar panels, said. The solar panels cut the prison's electricity needs by up to 70 per cent, he said.
Inmates said very few of them abused the authorities' trust. Anyone who breaks the prison rules is sent straight back to a closed prison.
"This is like a holiday camp compared to a closed facility," said another inmate, who asked not to be named.
Bastoey prison says on its website that its philosophy comes from an old Indian saying: "We don't own nature. We borrow and manage it in our lives, thinking about our descendants."