I've noticed in some maps, notable ones off the top of my head include Hong Kong Station (http://aotskins.com/viewtopic.php?f=72&t=7940) and a sort of beach resort (Of which I am having a hard time locating atm), there are pieces of, I'm guessing, geometry that are somewhat transparent. Like windows. I kinda want to know how to do that, I'm working on a map that I really would like to use them in.