A penal reform charity says the closure of HMP Lindholme's D wing shows why building large prisons 'makes no sense'.
The wing was forced to shut after inspectors said it was one of the worst they had seen.
"This is the latest in a series of damning reports published by the prisons watchdog in recent weeks, following scathing inspections of establishments such as Ashfield, Thameside and Hewell. It is deeply disturbing that conditions appear to be getting worse and worse at prisons across the country.
"Prisoners at Lindholme feel in danger. Many have been victimised and bullied. There are signs of racial tension. And yet little has been done to address the prison's underlying safety issues.
"This is supposed to be a training prison, a place where inmates are given the skills they need to prepare for life in the world outside. But prisoners on the category D wing had nothing to do. The classrooms were empty and abandoned. The public deserve better than to have prisoners lying idle in their beds for up to 22 hours a day.
"This report shows in sharp detail why it makes no sense to build large jails. The government should focus on reducing the prison population instead."
More top news
Jon Mitchell has the latest weather forecast.
South Yorkshire Police have given their reaction to the CPS decision to bring criminal charges against some former officers.
Six people are to face criminal charges over Hillsborough disaster - match commander faces 95 charges of manslaughter by gross negligence