Image sources:

• – Cave Houses:
  http://www.boncherry.com/blog/wp-content/uploads/2009/03/400http-dyimgcom-a-p-ap-20090226-capt2720ade3292b4c82abf353d83fc88948cave_home_motg1031.jpg
• – Missile Silo/Bomb Shelter Houses:
  http://www.odditycentral.com/wp-content/uploads/2009/10/missile-silo-house.jpg
• – Shoe Houses:
  http://www.ronsaari.com/stockImages/roadsideAttractions/hainesShoeHouse.jpg
• – Pyramid Houses:
  http://www.eyje.com/images/emimages/may2008/egypt-like-pyramid-house.jpg
• – Hovercraft/Spaceship/Ship Houses:
  http://listverse.files.wordpress.com/2007/10/hoovercr.-house-new-mexico-1.jpg
• – Tree Houses:
  http://treehouseguy.files.wordpress.com/2006/10/treehouse-fall-04-gif.gif