It might seem that impassable terrain is, well, impassable, and a blocked path cannot be unblocked except in map editor. Recently I have discovered that this is not always the case. Even during the game it is possible to do limited terraforming in a way that, depending on the map design, can dramatically affect the gameplay.   Here are the facts that make this possible:   When you place a building, the area below it and the surrounding rim about 3 tiles wide is converted to "ground" terrain; T