Locals call it the "Opa Gefaengnis," or Grandpa Jail.
The small 50-bed prison in Singen, a community of 20,000 people in southwestern Germany, is believed to be the only prison in Europe that specializes in aged inmates.
The minimum age here is 62, and the average age is 67. Sentences range from 15 months to life in prison, with the average sentence being five years.
The numbers of "gray crime offenders" have gone up considerably in recent years in Germany, where about 20 percent of all prisoners are currently over 60.
All of Singen's 50 male inmates committed their crimes after retiring, and those crimes are surprisingly similar to those in any prison. Singen's inmates have been convicted of fraud, drug smuggling and armed robbery. About a third are convicted sex offenders and six are serving life sentences for murdering their wives.
"The initial idea to have a special institution for elderly inmates, however, stems back to the early 1970s," explains Thomas Maus, who has been the director of the prison for 26 years.
"We realized back then that we had to do something to protect the elderly, more vulnerable inmates against discrimination and repression they sometimes suffered being locked up behind bars with younger and physically stronger inmates," he said.
He told ABC News, "A normal prison can be a terrible place for an older person. It can be a far more daunting experience for the elderly compared to younger inmates. Our idea is to not let them off lightly. This is a prison, after all, and they've got to serve their sentences. And we're neither an old folk's home nor a geriatric ward, but older prisoners need to be treated differently from younger ones."
And while the list of offenses is familiar to most prisons, life at Singen couldn't be more different.
The prisoners can wander freely around the three-story building between 7 a.m. and 10 p.m. They can bowl or play billiards, exercise and have physiotherapy for their old aching joints.
They are allowed six hours of family visits a month, and they are taken on country walks escorted by prison staff.
The physician comes once a week, unless called specifically, and a psychologist sees the inmates, mostly the convicted sex offenders, six times a week.
Those who feel fit enough can work at the prison's factory, packaging plugs and screws for a local company.
Maus told ABC News that the prison began 35 years, and its concepts still work today.
"I think we were right when we first started, and I think our system still works to the benefit of a growing population of older prisoners.
"Old age prisoners do have the same kind of common illnesses that other people their age have. But the stress levels here are generally higher and some of them are completely traumatized. That is especially true for first-time offenders," Maus says.
"Though they know they deserve to be punished, they often tell me they would not know how they would be able to survive 'normal' prison life," he said.
"The aging prisoner is usually more moderate in his demands and with regards to living together with other inmates," said Maus. "All he wants to do is to spend some time in freedom before his life is up."