I buried a 20 foot long steel seagoing container to be used as a combination root cellar, cool summer sleeping quarters and emergency shelter. It's excavated into a side hill so that the door end is exposed for entry. It's furnished with a single bed, wood stove, table & chairs and storage shelving. Here in central Alberta, Canada winter temperatures often drop to minus 40F. My Cave has been in use for 4 years now and even on the coldest days it stays above freezing with one small (3 sticks of wood) fire per day. Potatoes keep very well from one harvest to the next.
Step 1: The Excavation
The excavation was made with our small farm cat and backhoe. The far end was dug about 3 feet below ground surface and the bottom was then graded level from back to front. The width was about 4 feet wider than the container to provide working space.