I've always been obsessed with tree houses, probably because I never had one. That being said, I couldn't stop looking at these bizarre structures at the very tippy-top of the trees. For more cool tree houses, check out the rest of those on the Now That's Nifty post of Amazing and Awesome Tree Houses.
Link
My former teacher Mick Jurgensen has been building it for years. He used to bring the blueprints to class.
http://www.bigtreehouse.net/treehouse.html