The Ka'ba-ye Zartosht, meaning the "Cube of Zoroaster", is a 5th century B.C.E. Achaemenid-era tower-like construction. This enigmatic structure is one of many surviving examples of the Achaemenid architectural design.

The square tower is constructed of white limestone blocks, that are held in place by iron cramps. Mortar was not used in its construction. Each face of the building is decorated with slightly recessed false windows of black limestone.

The structure has one square inner chamber, 5.70 meter high and 3.70 meter wide, access to which is through a doorway with a decorated lintel in the upper half of the tower. The chamber was once accessible by a flight of steps, only the lower half of which has survived. The 1.70 meter wide and 1.90 meter high door was of solid stone that was originally firmly closed but has since disappeared.