The Cube by Wm F. Hogsten
Johnny Hooks knew he had been sentenced to the new high security prison, the "CUBE" was mandated by law for your second violation. When he awoke he never expected what awaited him in a prison such as history has never known. After one day he knew he would never come back, after the next he was positive, and very worried about the next five years.
The cube - an E-Book
A short story, that at this writing has a 5-star rating.