30 Prisons, some of which are dreadful places in which to be, whilst others can be surprisingly pleasant, as far as somewhere can be pleasant when you are not allowed to leave it. Some are short term places of confinement, others are where you will spend the rest of your life unless you manage to escape.
Most criminals who are locked up as a punishment or to await trial are just confined in regular cellblocks or jails, but not all of them. Some are so dangerous that ordinary prisons just will not hold them. Others have secrets that cannot be allowed to be spread, or their crimes are so dreadful that they deserve a greater punishment then normal incarceration or even execution. In yet other cases the ruler had a nasty sense of humour...
The PCs come across a town with a strange curse: Every morning, those who have grown up here wake up with the memories of someone else. They do not find this strange and have no idea it is happening. They calmly wake up and start these new lives as though they have always been that way.
The cause: A wizard who lived there was spurned by a maiden he was infatuated with. His attempt to manipulate her memories into believing they were already together and that she loved him went horribly awry.