FifthColumn's Curse of Strahd
Mists of Barovia
The Mists are a supernatural phenomenon unique to Barovia. The mists create a border through which is seems outlanders are able to enter, but not leave the region. they have a choking, enervating and disorienting effect on those who try to pass through them. The Outlanders, upon arrival in Barovia, were harried by the motile Mists toward the Village of Barovia and Durst House. when they emerged from Durst House, the Mists retreated. Madame Eva was seen passing through the Mists, seemingly unimpeded.
The Vistani claim to be able to travel through the Mists at will, but other than selling some fake potions which they claim will allow safe passage, they offer no details on how they do so or what is on the other side.
Madame Eva claims that Strahd controls the Mists, but that they also imprison him in Barovia.