The Stasi (East German Secret Police) prison Hohehschönhausen was used for politcal prisoners. A political prisoner is “someone imprisoned because they have opposed or criticized the government responsible”.
Some reasons for people had to spend years in these cells: subversive agitation, illegal border crossing (if they did not shoot you while trying), illegal connection (to the west), etc.
You can imagine how easily you ended up in jail. Once you’ve been there they observed, controlled and terrorised the rest of the lifes of the poor victims.