The Dark Tower

The Dark Tower is the Axle on which all worlds spin. In many ways it is more a concept than a physical building. As Roland enters and finds objects related to his own life one can assume that its structure (internally at least) is subjective to those who enter it. It is also notable that as it exists in End-World, that it is quite literally on the outer edge of reality (i.e., if one were to stand with their back to the tower and walk away from it in a straight line they would eventually run into it again at the other end of the world as well); and existing at all points in that outer edge as well, meaning there is no singular path to the tower, that in fact, if followed far enough, ALL roads lead to it eventually. Also the physical embodiment of Gan, or God.