I always fancied building a house into a hillside so only the windows were exposed. It would help cut heat losses as it never freezes below about 12" in the UK. It would also be cool in summer without needing active cooling.
Combined with controllable sunshades I reckon I could get energy requirement well down.
It'd be really cool to live in a genuine Hobbit House as well....
Been a couple of "Grand Design" type houses like this I recall.