There are many philosophies on punishment, but in medieval times, punishments were typically extremely harsh. Since prisons were (and are) extremely expensive, corporal punishments were very common. Things like cutting off the fingers or hands of thieves, removal of teeth, and the death penalty for crimes that seem relatively minor by today’s terms.
When creating a system of punishment, think about what those mean to your setting. Extreme punishments can be used to show how evil a country is, or can be used to show the character of the one who has to mete out that punishment. Think about Eddard Stark in Game of Thrones. He sentences people to death, but executes them himself. He even explains that a true leader should be willing to carry out the sentence so he doesn’t kill people too easily.
Prisons were typically only used for people who committed extremely minor crimes (such as accumulating too much debt), holding people until their sentences were to be carried out, prior to trial, or by the very rich and/or noble class. Again, these are extremely expensive, so a country that holds people in prison should be very well off or have some specific reason for doing so. In Myos, for example, they outlawed torture and the death penalty after the Druid Wars. This was partially due to the Treaty of Embers, which ended the war, and because of how ineffective it had been. In short, they were ashamed of what they had done and stopped it.
As with many things in fantasy, the use of magic changes how everything is designed. If magic is common, you’ll have to come up with methods to prevent people from simply teleporting in and out of them. If magic can control people, how do you make sure they aren’t being forced to lie? How do you prevent the wizard from using telekinesis or a sleep spell to escape?
Punishment can be used for great effect as a plot device. Make sure to keep it consistent (or for more fun, purposely make it inconsistent) and try to make it fun for your players or readers.
Next week, I’ll be starting a series that specifically looks at how magic changes the setting. Thanks for reading. See you next Sunday!