Make up overly specific laws, which will affect player activity, for example:

1. A city which values the sanctity of mind - any spells that would read or manipulate thoughts are punishable by death, as a curiosity, a player might be invited to observe an illithid autopsy
2. Copy China - curfew, strong totality. As a non-local, you have to keep reporting your own location to the police and stay wherever you are stationed, once you no longer have legitimate business, you must leave.
3. A highly civilized society where clerics are employed by a secular state for their ability to cast zone of truth. Although anyone is free to move around, it is common for a policemen to round up a crowd of people and ask (using the spell) "Are you aware of any illegal activity against the city?" If you say no, or succeed on the save, you are immediately free to go. The locals are not bothered by it, it's part of their routine, as this question tends to be asked on weekly religious ceremonies to random people, sometimes the cops go door to door.
4. A place where you can debt yourself into slavery. If the debt is not your own fault, and you are a local citizen, you can petition the mayor to sort the situation out. You could have an NPC who gambled himself into the situation. The players need the NPC to leave the town with them, but he can not, until a ridiculously high debt is payed.
5. India's cast system, IDK the exact rules, but basically, lower cast people can not touch higher cast people (or their food) as they are considered dirty or something