Abstract: A subterranean structure particularly adapted for greenhouse use and including a roof which can entirely close the enclosure or be moved to a position exposing the interior to natural light. Curtain assemblies are provided at the free end and sides of the roof to eliminate wind, rain or snow from entering the enclosure. Artificial light fixtures are mounted on the underside of the roof for providing artificial light when the roof is closed, and ventilation and supplemental heating means are provided to achieve the desired growing conditions in the greenhouse.