What does the search for Cairo represent to huck?

Cairo represented freedom to Jim. It was far enough among the "free states" where he wouldn't be hunted down. There he would make enough money to buy his wife back. For Huck, the search for Cairo not only represents a mysterious adventure (like searching for King Solomon's Mines) but he also wants Jim to be truly happy. While searching for Cairo, the two run into a thick fog. This fog adds to the illusiveness of Cairo and the sense of freedom it might offer.