My family used to live in an underground house near Casper, WY. That place was awesome. It was something like 12" of concrete, 18" of styrofoam insulation and six feet of earth. It had skylights for natural light and triple pane glass windows in the back. Place never got colder then 68 degrees farenheit (even at multiple tens below zero). It also had a well designed fireplace that could heat the whole house, and it was a big house. And when the wind was blowing 60 miles an hour out side, you couldn't even hear it inside. Incredible house, absolutely fantastic.