My players suddenly became curious about the cloudy/misty parts of the map. I can't remember reading anything about what's supposed to be there except that the northern mist part is the elven place (Stilldimman in Swedish, don't know what it's called in the English version). But there are four other misty regions - "Mistra pass" in the southwest, in the middle of the mountains just north of that, in the northwest and on the plains in the east near Falender.
I'm guessing it's a "it's up to you" situation, so I'm curious what other DMs have done.
Bloodmist? Impassable terrain? Just really thick eternal mist?