The Primitive Earth Map extension includes a map of the ancient earth. Like the normal playing card, it is double-sided and can be assembled into four different maps. This radically changes the game. Each turn, a Glacier piece appears in one of the polar zones and moves south (or north). As the game progresses, the glaciers begin to constrain the actions and movements of the players, until everyone is forced to move to the equatorial regions, which quite naturally results in a bloodbath.
If you like massive clashes and forced battles in the middle or end of the game (even more than in a normal Cthulhu Wars game), this is the expansion for you.