Gloom Boxes

Here's an idea I wrote for Shadowfell, could work with Hades or the Plane of Shadow:

The Gloom Boxes: The Gloom Boxes are a collective term for the jails, asylums, and most unfortunately orphanages and refugee camps that simultaneously exist in the world and in the emotionally draining glooms of the Shadowfell. Designed to make the charges within their confines more tractable, many of these facilities are now haunted ruins left in disrepair. They might simply apper abandoned during the day, but one quickly realizes the anger when the sun goes down and the undead reclaim the places of their cruel deaths.

Those Gloom Boxes that are still intact are places where the charges seem drained and docile, and while heroes should be quick to free the innocent and the youthful, there is some truth that incredibly dangerous prisoners are controlled by keeping them in these arcane jails. Of course, why some of these dangerous criminals need to be kept alive is another question - for some communities it is done because they cannot bear to their loved ones a death sentence. For others it is because there are family connections, or perhaps some noble or wizard hopes to draw out secrets of buried treasure or lost magic from the killer or thief.