Though Frank Lloyd Wright never built earth homes in hills, his autobiography suggests he might’ve approved of them. “No house should ever be on a hill or on anything,” the architect wrote. “It should be of the hill. Belonging to it. Hill and house should live together each the happier for the other.” Earth-sheltered homes—which typically feature either underground construction or homes built into slopes with soil against the walls and on top of the roof—are among the oldest forms of buildings, dating back thousands of years. Because the surrounding land acts as a thermal mass that insulates the property, the US Department of Energy recognizes them as energy-efficient form of construction. Further, the houses are often less susceptible to extreme temperatures outdoors. So perhaps the best way to live with the earth might actually be to live within it. But can residing surrounded in dirt actually be comfortable? Below AD visits seven exciting examples of earth homes that prove underground living can be as stylish as it is environmentally friendly.