I was just googling it and came across this story about the Bellavista Prison in Medellin: New Life in a Culture of Death. It's a CT article from several years ago, but I still found it really compelling.
Here's the first two paragraphs:
I encourage you to read the whole thing -- I think you'll find it's a powerful testimony to God's power to influence whole communities with the peace of the Gospel.
Thousands of red brick homes, the shade of dried blood, enfold mountainous Medellín like the memory of an infamous killing. Death, Colombians say, is pan diario (daily bread), as commonplace as that staple of life. This culture of death yields 3,000 homicides a year in Medellín alone, by knife, machete, pistol, machine gun, grenade, and bomb.
Where Medellín's mountains touch the valley floor stands Bellavista. This prison complex, constructed of that same blood-red brick (painted blue and white) is where hundreds of Colombia's worst criminals and guerrillas have met an evil end in vendetta slayings. Fourteen years ago, violence reigned over Bellavista. But through the persistent efforts of Christians, Bellavista has become a spiritual clearinghouse where Colombians, deeply divided along religious, economic, and political lines, may reconcile their differences.