On the outside, the Summit House—designed by ParkCity Design+Build—appears to be a hardy mountain retreat sheathed in weathering steel.—and it is. But it's not only that: The dwelling was also designed with rigorous eco-friendly standards in mind. As a Passive House, its walls and windows were carefully engineered and super-insulated to stop heat leaking outdoors. This means the house is 90% more energy efficient as compared to a normal design, an especially impressive feat given its location in often-frigid Park City, Utah. That efficiency doesn't come at the cost of comfort, as evidenced by cozy interiors and large windows that let in natural light.