I have never had a real live root cellar, the underground type that is. The guy we bought our home from built a "cold room" onto the side of the attached garage. 'Bout the size of a walk in closet, thick insulation all around, shelves on all walls, a window air conditioner built into one wall. Unless the A/C is on about nine months out of the year (we are talking central CA here), it is worthless for anything but dry and canned goods. And running that A/C all the time can get expensive. Other than that, I think you need to dig a hole in the backyard...