The coolest fog I remember being in was in Honey, Hidalgo, Mexico. Honey is a small town in the mountains near Tulancingo, Hidalgo, founded by a group of British ex-pats. It has the feel of an English village, sorta. The groves of pines looked particularly eerie at dusk with the fog rolling through. Fortunately we weren't far from our vehicle when the fog surrounded us and reduced visibility to about one foot. Come to think of it, Mexico City and all it's air pollution is not that far from there. Hmmmmm. I wonder how much effect it had on that fog?