I just saw this guy (Walter R. Tschinkel, of Florida State University) on the History channel, and the stuff he's doing is way cool. He makes castings of ant nests. Pours dental plaster or molten metal down ant holes, let's it set up and then carefully digs it out. The resultant structures are mind-blowing. Very cool. And it's for science. Without this sort of casting, I imagine we'd have no idea at all about the structure of ant nests! According to the paper, mature nests of the species he studies can be 3 meters deep (which I guess is about the size of the one at left).
Click the title for a link to his paper, which contains a load of pics at the bottom. Say... wouldn't it be cool to make these for sale? I wonder how much you'd have to charge to get a reasonable turn on your time?