Curse of Strahd
The Mists of Ravenloft
The land now called Barovia now exists within a demiplane formed by Strahd Von Zarovich’s consciousness and surrounded by a deadly fog. No creature can leave without his permission, and those that try become lost in the mist.
Strahd Von Zarovich allows the Vistani to come and go as they please because he admires their lust for life and their willingness to serve him when he needs them. He also owes an ancient debt to the Vistani people. As a soldier centuries ago, he suffered a grievous injury in battle, and the Vistani tended his wounds and returned him safely to his family without making any demand for payment.