Well I have never been to prison, but I heard from a friend of a friend of a friend sort of thing that the lower security ones, that exist to support the mass of criminals convinced that aren't really a major threat to anybody, are close to motels, and not the 'don't drop the soap' hell holes they are made out to be in the movies.
Were I homeless with no chance of a turn around, I would try my luck.
In the US, there are five levels of prison security:
Minimum: No violent criminals, or at least not ones that generally pose a threat to other people. Nice place, more like a college dormitory than what you'd think of as a prison. Things are nice enough here, you might even get internet if you behave! (So someone in one of these prisons could very well be reading this sentence.) Somtimes there's a single lightly-guarded fence, but a lot of them don't even bother. The conditions are pleasent enough that most people wouldn't risk escape, as this can get you bumped up to medium security. Your fellow prisoners probably aren't going to hurt you, embezzlers, identity thieves, and light drug users aren't really known for violence. You have a good chance of ending your term early if you don't act up, especially considering the number of rehabilitation and community service programs available from this security level. The few guards that are around probably won't end up killing you in any situation.
Medium: Some violent criminals, but only a few killers as that's usually maximum security. The others are those who've commited
a lot of severe non violent-crime. Communal living, with bunks and lockers for personal posessions. Most of the facilites are communal too, so don't drop the soap. You'll mostly be around other prisoners, and a few guards. At night, only a few will be keeping watch as the amount of trouble here is limited. Join a prison gang if you want to avoid the violent people's wrath, though. Most people here are getting out eventually, assuming they don't die in the next few decades. Double-fenced perimeter. Guards usually use less-than-lethal weaponry here.
Maximum: Boy, you sure screwed up to get here. You only get out of your cell for one hour a day, but at least you get to move about the cell block. Don't bother trying to escape, the security is all controlled by a remote terminal that isn't connected to any cell block. Very few here are ever going to be free again, as sentences are usually life or periods of time that will go over your lifespan. Triple-fenced perimeter, with a lethal current running through the outermost one. Oh, and a metric ton of razor wire.
Supermax: The worst of the worst go here. You might not end up in solitary, but you will be kept seperate from other prisoners. 23 hours a day in your cell, one hour to exercise in a cage outside. Dozens of guards with shoot-to-kill orders and multiple fences and security doors stand between you and freedom. No one leaves here except in a body bag.
Ultramax: You do not want to be here, ever. 24 hour solitary confinement, no chance of improvement or escape. This is how you will live out the remander of your days, completely alone. You'll probably go insane sooner or later. Death would probably be preferable to this. Only exists in the worst sections of ADX Florence, the only federally run Supermax prison in the USA. Coined term, not technically a real security level.
Now, this is how it's
supposed to work. Problem is, there are so many prisoners and overcrowed facilites that sometimes security compromises have to be made just to hold all the criminals around. Keep in mind that these descriptions are what I knew about prisons beforehand and some light research, so don't take what I've told you as absolutely true.