Perched atop a high cliff in the heart of the city of Khorramabad, the majestic Falak-ol-Aflak Fortress stands as one of the most recognizable symbols of Iran. Also known as Shapur-Khast Castle, this ancient citadel was built during the Sassanid era in the 3rd century AD and served as an impregnable defensive outpost for centuries.

The name of the structure translates poetically as "Sky of Skies". One theory suggests this name was given because of its eight massive towers, which in ancient times may have symbolized the celestial spheres. The citadel covers an impressive area of over 5,300 square meters, and its walls, built of stone and brick, reach a height of 23 meters, showcasing the power of ancient engineering.
One of the unique features of Falak-ol-Aflak is its hidden moisture control system. A network of channels was laid beneath the foundation to drain groundwater, protecting the masonry from decay for over 1,500 years. At the foot of the hill, the Golestan Spring flows, which once supplied the castle's inhabitants with water via a deep 40-meter well that still functions today.