The three films I found most impressive at #berlinale all happen to be set in prison:
#GhostInTheCell
Indonesian horror comedy film with very artistic kills, a lot of social criticism that is so obviously thrown in your face that it's actually good again, and the humor is also pretty much spot on.
#Animol
At first glance, the description makes it sound like a typical prison drama, but it is so perfectly acted and emotionally engaging that I was very moved by it. The bond between the two prisoners is also kept subtle most of the time, which only makes it all the more powerful.
#TheOtherSideOfTheSun
I definitely can't recommend this film to everyone - it's really very hard to watch. It makes you doubt humanity even more than you already do. But in some ways it also gives you a little hope to see how people stick together and support each other in such extreme situations.