To see these structures need to be in 22 states located in the Americas, Europe, Asia and Africa. Today in our photo gallery - the most unusual houses in the world.

With the population growing more and more each year, it was only a matter of time before people started building their homes underground like Hobbits from the Tolkien tale. Mankind started off living in caves, and now we realize that "earth homes" are actually a very eco-friendly way to live. These ten underground homes are so amazing they might make you want to set up camp underground too!
Cave House in Festus, Missouri
This modern and energy-efficient 15,000-square-foot home is built within asandstone cave in Festus, Missouri. Built by Curt and Deborah Sleeper, the home features modern interiors that blend with the natural unfinishedsandstone walls. Thanks to geothermal heating and clever design, there is no need for air conditioning or a furnace to heat/cool the home.