Yakhchāl is an ancient type of evaporative cooler. 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.
The Yakhchal itself was made out of a special mortar called sārooj, composed of clay, sand, lime, goat hair, egg whites, and ash mixed in a special proportion which made it extremely resistant to heat transfer. In other words the inside stayed cool, while heat from the outside was prevented from entering the building because of the thick insulated walls.
The ice was then used to chill treats for royalty during hot summer days and to make faloodeh, the traditional frozen dessert.
Source: Ultra Facts