Basement house, Minnesota, 1947,
Via Honestly_ on Reddit, goo.gl/HDZPdJ who says:
Due to major post-WWII housing shortages, some families excavated a basement on their lot and lived there until they could afford to build a house.
Photo from Minnesota Historical Society, published in Minnesota Modern, which covers midcentury modern buildings in the area.
Looks practical – cozy in the winter, cool in the summer. Though in the winter ventilation would be a problem when it gets piled high with snow.