I expected that after my first time behind bars (I was a visitor to HMP Birmingham last week with Debating Matters) that I would be writing primarily about the ludicrous, wasteful number of people we hold in prison.
Britain has the highest rate of imprisonment of Western European states, and the number of prisoners has nearly doubled since 1993, despite the crime rate going down significantly.
The average prison sentence is three months longer than 10 years ago, and for indictable offences 18 months longer, yet nearly half of the people entering prison are sent there for six months or less, even though it's well known that these sentences are far less effective in reducing reoffending than community punishments.
And the crowded conditions of this Victorian prison were obvious from the start of our visit.
We conducted a "Question Time-style debate", then listened to the final of the prisoners' debating competition in the prison chapel, in the oldest part of the prison.
We walked past obviously tiny cells to reach that. A staff member pointed out to me drily that these used to hold one Victorian inmate, but they hold two modern prisoners. "And the prisoners are a lot bigger now."
That degree of crowding is having well-documented impacts on the ability of prisons to rehabilitate - to provide the education and training opportunities, the chances to for prisoners to develop new kinds of behaviours and understanding that can ensure they can get their life back on the rails.
As one of the prisoner debaters said, in an excellent debate on whether prisoners should have the vote, "you've got a lot of time to think in prison".
But for that time to be well used - for thoughts to be guided on to different paths and useful directions - there needs to be staff time, facilities and opportunities. (On that subject of the vote - one of the debaters made a very good point: "prisoners go to jail for breaking the law, but Britain is breaking the law in not giving them the vote".)
Vicky Pryce, one of my fellow "outside" debaters, and the only one of us with experience of being a prisoner, was particularly passionate about the need to follow other countries in allowing prisoners to access online learning resources, something for which the Prisoners' Education Trust has been pushing.
She was also rightly outspoken on the way in which imprisonment of women is particularly damaging - an issue on which I've campaigned. I really hope that Debating Matters will be able to repeat this event in a women's prison soon.
But I left thinking on an even broader scale, of the waste of lives that are allowed to go off track - the young people for whom life starts to go wrong in their early school years, and then just keeps getting worse.
Watching the prisoners debate - seeing the skills and abilities that had blossomed through only two training sessions, not just from the speakers but the teams who'd prepared the cases - what was evident was there was real talent here, abilities that previously had never been given the chance to develop. These are wasted capacities that our society badly needs to access.
Edwina Curry and I (who've had lively exchanges previously), were both on our best behaviour - modelling conflict carried through in a constructive way. And that's exactly what the prisoners were also doing - something they said hadn't been the experience of their previous lives.
And these prisoners were certainly using their time in thinking about their own experience and the state of Britain today.
I wasn't sure what reaction I'd get when during the debate I raised the issue of prison (and broader criminal justice) privatisation. But the principle that the coercive power of the state should never be privatised (and the reality of the activities of the company for which they work, G4S) couldn't be ignored.
I did wonder if it would be of interest to the prisoners, and it certainly was - it got the first big cheer of the question time, and was the subject of considerable discussion over lunch.
I hope the staff got the message that when I criticised private prisons, I wasn't criticising them as individuals. The governor Pete Small and the team here are obviously doing good things at the jail - included an elected advisory council of prisoners and Debating Matters' presence (a first).
There should be many more, steps like this, much more action to make our prisons useful, rehabilitative places. But what is also needed is far more useful steps outside prisons, to set young lives on different paths.
The Netherlands is closing prisons because of lack of demand. That's what Britain should be aiming for, not just by replacing the failed model of short prison sentences with community punishments, but also by investing in education, by tackling poverty, by building opportunities to ensure fewer lives end up on the wrong path.