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if you buy Planet Coaster - 9,49 € , you wont even have to worry about what to do with the rest of the money

The Orange Box - 1,89 and Portal bundle - 2,23

if youre missing everything from the Orange box i would prefer it
You get alot of Trading cards back while playing or idling
[You get TF2 premium ] i got it from purchasing the orange box back in the days and you get some items to sell back for just logging into the game from the Events .
So you could probably make Profit .

The Portal bundle is a great deal and Prison Architect ist fun too.
3 good games for a bit under 10€ is not bad.

Darkest Dungeon is 9.99€ if you like that kind of game.

Depends on your favorite genre.
Do you like strategy games? Then, Prison Architect will keep you busy for a long time.
Do you like puzzle games? Portal is awesome, if you do.
Orange box has some good games in there as well. some are really old, though.

The Orange Box and Portal 2 are cheap, damn, if you never played those gems you should totally get them (being the first Portal included in The Orange Box, you should get the latter first, then Portal 2). If you are sure about Shelter, you may consider the complete bundle at 2.79€. Cheap AAA games worth the money are Tomb Raider at 3€, and RAGE and Dishonored at 2,5€. If you like to have fun, consider also Postal 2 + expansion at 2€.

There are a gazillion of indie games discounted by 80-90%, it's hard to pick some without knowing your preferred genres; few examples from my WL: Virginia and Age of Gladiators 0,99, or Pathologic HD 1,94.

hollow knight

Hey if you decide to get Prison Architect then it may be cheaper to buy it within this bundle than buy it alone...
If you own scanner sombrero already

http://store.steampowered.com/bundle/1905/Introversion_Complete_Bundle/

Portal games are really awesome: if you never played them, it's a no brainer.
I played Prison Architect long time ago and just came back to it yesterday. It's way more polished and complete, obviously made with love and effort.I can't tell if you'll be bored with it soon, but you should have fun before that for sure :)

I LOVE Prison Architect. It's every Simulation fans wet dream because the simulation is so in depth and the longer you play the more you will understand the mechanics and how they interact.

Let's take the prisoners for example: Beside the reason why they end up in your prison everything gets simulated accurately. Depending on the way you run your prison they will be easy to control or act up and start fights, destroy the furniture or try to escape.
When you look at individual prisoners you can see how long they've been in your prision and what happened to them f.e. what infractions they've had or which rehabilitational programs they've attended. And when a prisoner fails one of their rehab classes there's always a logical reason for that: maybe their cell is too far from the classroom so they will miss the first half of most classes, maybe they can't concentrate properly because they are intimidated by guards with shotguns or dogs patrolling next to the classroom or maybe they're just plain stupid or have a short attention span.

Or as another example when there's lots of fights in your prison you could look into the reasons behind this and improve conditions so prisoners are more content or you take the opposite approach and look into how contraband and weapons get smuggled into your prison and put an end to that. Fewer weapons, fewer fights. The choice is yours.

It's hard for me to put it in words how much I love this game. The only problem is once I start playing I can't stop :D

From the games you listed definitely Orange Box and Portal bundle. Keep Talking and Nobody Explodes is fantastic if you have a friend who would play it with you. Laughs will be had, keyboards will be broken. :D

If you like challenging platformers by any means, Super Meat Boy is a no-brainer for 1,39€