Yeah, broken glass made out of booleans. It is possible to import the tower, set the attributes of each single part to "positive", take a huge rock or terrain and set it "negative" and group them. Works pretty good. :) --- Today I modelled some sidetowers which can be applied on the outer walls. And every other roof or floor part can be applied to the sidetowers - everything is compatible, it only must be scaled down because the sidetowers are smaller. :) J.