Mists of Ravenloft

A deadly fog surrounds The Domain of Barovia and engulfs any creature that tries to leave. Even flying creatures are subject to the fog’s effects, which are as follows:

• A creature that starts its turn in the fog must succeed on a DC 20 Constitution saving throw or gain one level of exhaustion (see appendix A in the Player’s Handbook). This exhaustion can’t be removed while the creature is in the fog.
• No matter how far a creature travels in the fog, or in which direction it goes, it gets turned around so that it eventually finds itself back in Barovia.
• The area within the fog is heavily obscured (see “Vision and Light” in chapter 8 of the Player’s Handbook).