Winter Queen

An ancient elven legend tells the story of the Winter Queen, who used to cross the land in a sleigh drawn by white horses during blizzards. As she went, small shards of ice flew about. Those who were hit by one of these shards were forever doomed. Nothing in this world made them happy any more, everything looked sad, disgusting and dull except the whiteness of the snow, the frost and the ice. They left everything behind them to search for the Winter Queen, forever wandering without being able to find her. And thus they died attempting to fulfill their dream.

According to Geralt, the Winter Queen was actually nothing else than the dreaded Wild Hunt, which haunted certain forsaken lands, enslaving its inhabitants' will and making them its thralls.