Walipini tour

Walipini, or underground greenhouse is an incredibly effective way to grow food year round in climates subject to below freezing temps.
The sun's light and heat comes through the plastic roof and is trapped inside, heating up the walls and keeping it warm (above about 50 deg) all night.
The other advantage is the protection from wind as there are no external walls.

http://www.treehugger.com/green-architecture/build-underground-greenhouse-garden-year-round.html