Ravenloft

As taken from Storm Giant Games' summary

Dark, gloomy castles, desolate landscapes, black clouds racing against the moon - these are the trappings of any gothic novel. Stories replete with mystery, fear and desire. Novels such as Dracula, Frankenstein, The Strange Case of Dr. Jekyll and Mr. Hyde. Plots involving strange birthmarks, family curses, ancient secrets and supernatural figures. These macabre themes can creep into any campaign, in any world - but in Ravenloft, these themes have reached poisonous fruition.