Ravenloft, a
fictional setting from the
Dungeons & Dragons role-playing game, is not a world per se, but a collection of 'domains' brought together by mysterious powers known only as Dark Powers, which separate one domain from another. Each land is ruled by its darklord, who has committed a crime so foul as to attract the attention of DP and be imprisoned, seemingly forever (though some can be killed and replaced), in their domain, which they aren't able to escape by any means magical or mundane. The Mists play with them by denying their most coveted dream, be it love, glory in war or the defeat of their enemies.
Ravenloft is primarily a gothic horror setting. DMs are encouraged to use scenes that build apprehension and fear, culminating in the eventual face-to-face meeting with the nameless evil. Characters have a much greater significance attached to their acts, especially if they are morally impure, as they risk coming under the influence of the Dark Powers and gradually transforming themselves into a figure of evil, in the form of failed power checks.