People Fixing People Fixing the World.
I'm Mayra Anubi, and this is People Fixing the World from the BBC World Service, a program that finds solutions to some of the biggest problems we face this week.
Our search for solutions is taking us inside a place that most people try to avoid, prison.
According to recent research by the United nations, There are nearly 12 million people in prison around the world.
And many prisons can be really dangerous, with suicide and murder rates far higher than the general population.
Also, a quarter of men and one in five women report being physically assaulted, either by guards or fellow inmates during their incarceration.
And not only that, but after rehab release, many also reoffend.
So today we're finding out about projects that are trying to stop violence in prisons and get ex inmates to stay away from crime.
And what better place to start than in the US The United States has the largest prison population on earth, with over a million people behind bars.
It also has one of the highest rates of reoffending, with two thirds of former prisoners engaging in crime within three years of getting out.
But in Philadelphia, a city to the northeast of the country in a state called Pennsylvania, one prison is testing a very unusual model that they hope will eventually bring down these numbers.
We sent our reporter Ben Wyatt to find out how it all works.
So I'm on a piece of industrial land just by Philadelphia Airport.
You can hear the planes overhead, big sign in front of me, it says Pennsylvania Department of Corrections, the State Correctional of Chester.
So I think we're in the right place.
Chester Prison may have all of the usual security precautions of a state penitentiary, like these steel cage double doors at its entrance.
But not everything in this prison is as expected.
Where do you want to go first?
Just around you.
If you want to do a run.