Ravenloft is a dark gothic horror campaign setting, consisting of a number of mist-shrouded extradimensional spaces known as the Domains of Dread.
Each domain acts as inescapable prison, trapping a powerful and evil Darklord in an ever changing reflection of the dark lord's psyche.
The malevolent mists of Ravenloft can swirl up unpredictably and transport other people into a domain.
They also form a thick, white, and impenetratable barrier that prevents travel between domains, only rarely permitting passage from one domain to the next.
Mistrealm is a homebrew campaign setting that is similar to a Ravenloft domain.
Mistrealm is also my personal collection of miscellaneous unrelated links and articles on various topics.