MR K, as he wishes to be known, was in HMP Nottingham for four months of his eight-month sentence for sexual assault.
The 36-year-old from Derby was released last week and wanted to tell the Post what he saw when he was inside the prison and how grateful he was to be back on the straight and narrow.
Mr K said: "It was an absolutely horrific experience. A free-for-all of drugs and violence.
"Prison hooch was being brewed and readily available. There were drugs everywhere, mainly cannabis, and you could see it in people's eyes.
"There were quite a few incidents of violence. The was always an alarm going off and every day the staff were running to a fight.
"But because they were so under-staffed, if there was trouble on another wing, they would have to lock up those who had behaved well all day to staff another wing. Then those would be angry and rebel at the slightest thing. Some days it was ridiculous and I would be in my cell from Tuesday lunchtime until Thursday evening, going without even a shower for 48 hours.
"The amount of times I saw people come back when I was there. They would go out and come back the next week. When they get no direction, no guidance and pushed out into the big wide world with no prospects, they think 'why try?'
"The biggest thing is if they go out, realise no-one is going to give them a job and they are going to have to live on benefits, they think at least inside I have a bed and food.
"Then there is such low morale with staff too. They told me they were just the staff, they have got management above them and they just have to do what they say. They see it as a dead end.
"I don't mean to get in trouble again. But I am lucky. I am starting back at my job and I have got my family and kids around me. For others, there is no rehab. Just coming out with all their friends in prison and no-one knows them or wants to talk to them. There is no support. It was a massive learning curve and very frightening."