Chronicles of Khaldun: Crux of Eternity
The Domains of Dread
Floating like soap bubbles through the Shadowfell, the Domains of Dread are a series of loosely-connected demiplanes. Their origins are mysterious, but their purpose is clear — Domains of Dread are prisons for darklords, and any other hapless mortals who might have fallen into them. They are twisted, sinister places, full of dangers and difficult to escape.
Barovia is probably the most famous Domain of Dread known.