A Tune To Dance To
Ravenloft, the Domains of Dread
Located deep in a twisted part of the Shadowfell exists the darkest of the Domains of Dread. Some exist further out in the Shadowfell, but they are pale comparisons to the Domains of Dread ruled over by the mysterious entities known only as the Dark Powers.
Each Domain is ruled over by a Dark Lord. The Lord has powers over their land and most have the ability to seal the borders of their lands to stop people leaving their domain.
Surrounding the borders of the Core, the Clusters and the Islands are the Mists. They are unknowable, they are mysterious and the are dangerous. The only people who have any control over the mists seem to be the Vistani, their secrets are held tight to their chest and they are not sharing them with anyone.
The Ravenloft FAQ from the Fraternity of Shadows website is a good place to start for people new to the setting.