Below-ground homes are great environmentally, since they use less energy. But while they're cool, both literally and figuratively, they're expensive to build. That is, unless someone's already done the work for you. Someone like, say, the US Government. So whether you're looking for a really cool house, or just want a pre-built supervillain lair, there's not much that can beat an old 1960s ICBM missile silo complex. While you may not get one exactly where you want, you can't argue with the awesome that is 20th Century Castles (Missile Bases).