It's a safe room in the basement of our house.
6'x20', concrete walls and ceiling, steel fire door, storm shelter type of thing.
We use it primarily for storage. Keep it stocked with canned goods, dry foods, water, etc.
Sounds really nice . I wish our basement was cold enough for a root cellar. Its a downstairs walk out, unfinished room in the back for storage and canned god pantry, furnace etc. I tried two big coolers with thermometers in the attached garage this past winter. Worked really well until late January. Now I think I will just do one.