The ice house - a yakhchal - is an ancient natural refrigerator.

Above ground, the structure had a domed shape, but had a subterranean storage space; it was often used to store ice, but sometimes was used to store food as well. The subterranean space coupled with the thick heat-resistant construction material insulated the storage space year round. These structures were mainly built and used in Persia. Many that were built hundreds of years ago remain standing.

http://en.wikipedia.org/wiki/Yakhchal