Ravenloft
Ravenloft is a campaign setting for the Dungeons & Dragons roleplaying game. It is an alternate time-space existence known as a pocket dimension called the Demiplane of Dread, which consists of a collection of land pieces called domains brought together by a mysterious force known only as "The Dark Powers". Each domain is mystically ruled by a being called a "Darklord".
Setting
Ravenloft is primarily a Gothic horror setting. Dungeon Masters 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 (through the game process called "dark powers checks") and gradually transforming themselves into figures of evil.
The magical mists of Ravenloft could appear anywhere in the Dungeons & Dragons universe, drawing evil-doers (or player characters) into the Ravenloft setting. One exception is the 'phlogiston' of the Spelljammer setting. The phlogiston blocks all planar travel, but the mists can appear in deep space inside crystal shells, according to the Complete Spacefarer's Handbook.