Each of the units is pretty small by itself, with only about 475 square feet of floor space. But you can link these homes together, or recruit your friends to be your neighbors and pretend you're living in a Smurf village. Just check out the city of Kumamoto's Aso Farm Village, which sports 480 of these weird domiciles.
Suzu via Wunderground
Or possibly Bedrock.
Considering that they'll probably never crumble from age or weather, we're pretty sure the only thing aliens will find on Earth a million years from now are the Great Pyramids and these Styrofoam tit-houses.
The Luxury Caveman House
In 2004, Curt Sleeper purchased Caveland in Festus, Missouri -- a former mining site turned concert venue -- on eBay. Once the structural and property line inspections turned out aces, he and the family went about the enormous task of tossing a house into the Flintstones-like crevice you see below.
"We're gonna need bigger nails."
After four years (and numerous nights of sleeping in tents), the Sleepers' troglodytic dream home was finally complete. Because they left the interior sandstone walls more or less natural, the Sleepers added indoor coverings where crap was occasionally shedding off the walls. So while opening umbrellas indoors might be considered unlucky, they beat the hell out of sandy eggs.
They're only one lava pool from having a supervillain volcano lair.
On the plus side, the Sleepers pay precisely jack and shit for heating and air costs: Geothermal heating and the cool cave walls keep the temperature regulated. The place can get damp pretty fast, though, being a cave and all, so the Sleepers have to run three huge dehumidifiers, which produce about 300 gallons of water a day. Prehistoric man didn't have to put up with such annoying feats of engineering, but then again, the Sleepers don't have to worry about saber-toothed cats traipsing around their backyard.
For more bizarre human creations, check out The 8 Strangest Communities on the Web and The 6 Most WTF Special Edition Comics Ever Released.