World's Wildest Houses VII

Freiburg, Austria

German architect Rolf Disch built this environmentally conscious abode for himself in 1994. Named for the Heliotrope, a class of plants that turns its leaves constantly to face the sun, the home is designed to perpetually rotate on its central axle. Here's why: One half of the building is all windows, allowing the sun to naturally heat the interior during cold months. The other half (shown) is heavily insulated to disperse heat during the summer, and keep the interior cool without air conditioning.

Meanwhile, the roof sports a solar hot water system that heats harvested rainwater. Not eco-friendly enough for you? Solar roof panels also generate between five and six times more energy than the house requires, making it an "energy positive" house.