I'm not sure why, but tree houses are cool in a way I can't quite put my finger on. I know when I was a kid, it was just cool to be up that high in the air. Maybe it's something about being high-up, or above the things going on below that make tree houses appealing. Maybe there's a kind of security we feel when were above the ground and, at least partially, away from it all. I think it's this feeling that makes people want to build tree houses as adults. There's a comfort to tree houses that we...