If you think you are going to like this game, you probably will! Prison Architect is pretty much exactly what it sounds like it is going to be. It's a prison simulation game where you manage a prison. But it does that very well!
There are different ways to play but in one way you get a certain number of minimum, normal, and maximum security prisoners dropped off every day. You need to make room in your prison for these guys, you need to keep them happy, and you need to make sure they don't run away or kill each other.
To start off you can either build a large holding cell or smaller individualized cells (the individual cells are much more expensive but it keeps the prisoners happier). Each prisoner has needs like the need to shower, to eat, to sleep, to go out to the yard, to talk to their family, etc. You can see these stats on a per prisoner basis or as an overall stat at the top of your screen. The more unhappy your prisoners are the more likely they are to try to escape, to cause a riot, to kill people, etc.
The other thing you need to keep in mind is money. You are running a for-profit prison after all. You can get money from grants at the start of the game (they are kind of like mini quests where you get half the money up-front and the other half once you complete the objective) and you also get money depending on the number of prisoners you have. You spend money every day on things like food, guards, other staff members, etc. You can hire less staff members or reduce the quality of the food but there are risks to doing those things.
So what's the endgame? Once (and only once) you decide your prison is profitable enough, you can sell it. The game gives you a monetary score depending on how well you did. You can use this money to start your next prison and make it even better.