Slide 23 of 33: Carved out of a massive rock on US Highway 191, this unusual structure started life in the 1940s as a small alcove for the owners’ kids to sleep in. It gradually expanded into a 5,000-square-foot (464sq km) home with 14 rooms. The unusual ‘house’ is usually open for tours so people can see how the Christensen family once lived. Things get even more bizarre with an on-site zoo, roamed by zebra, camels and bison.