It’s natural cold storage. A place to store excess produce from your garden at no-energy, low-cost for up to half a year. It works on the idea that when you dig down anywhere, the subsoil maintains a uniform cool temperature no matter the high or low temperature outside. Over 100 different kinds of crops can be kept in this easily made traditional storage. Included are plans for many types, from elementary earth pits to full-fledged basements. And instructions on how to prepare the harvest. These principles can also be used on urban homesteads. This is the definitive book on the subject.
I dug my cellar in the side of a hill sloping to the south, where a woodchuck had formerly dug his burrow, down through sumac and blackberry roots and the lowest stain of vegetation, six feet square by seven feet deep, to a fine sand where potatoes would not freeze in any weather….I took particular pleasure in this breaking of ground, for in almost all latitudes men dig into the earth for an equable temperature. Under the most splendid house in the city is still to be found the cellar where they store their roots as of old, and long after the superstructure had disappeared posterity remark its dent in the earth. The house is still but a sort of porch at the entrance of a burrow.
— Henry David Thoreau Walden
The dirt-floored root cellar in our old house.