I was in a little town in the South of Mexico a few years back when I inadvertently found the local prison.
It didn't take a Lonely Planet or much investigation to find the place. It was smack-bang on the plaza in the middle of town and might well have had its plans drawn up by a child.
It was a jail, not a prison. A rectangle with enough space for six or eight squatting prisoners, three stone walls and a full-frame iron-bar front, just like in the movies.
The forlorn men inside could watch the world go by and the rest of the townsfolk could stop in and see who had got drunk or stolen a chicken. A set of stocks wouldn't have been out of place.
Medieval, that's how it looked. But, as my travelling companion quite rightly noted, Western versions aren't much different.
Prisons are necessary. But if you consider humanity's advances, you have to concede they're a bizarrely crude form of treating human beings.
The US has had private prisons for a while and, naturally, it has led to a few issues.
Judges have been caught taking kickbacks from prison companies in exchange for locking people up.
Mandatory minimum sentences have made the US prison population far and away the largest on Earth.
The vast majority of those unfairly affected are African-American and poor. The US prison system actually makes Serco look all right.
I have a libertarian mate who says privatisation is a good idea. We just have it the wrong way around.
Pay prison companies, he reckons, for the number of their former inmates who don't go on to reoffend. Every year that a former inmate doesn't reoffend, the Government rewards the prison company with a fee.
Economically, it's cute, but it's a hard political sell.
Instead, here's an idea: perhaps we just wake up and acknowledge the only way to make the world's crudest institution even more archaic is to allow people to profit from locking other people up.