Falak-ol-Aflak is one of the most impressive castles in Iran. It is situated on the top of a large hill with the same name within the city of Khorramabad, the regional capital of Lorestan province. This gigantic structure was built during the Sassanid era (226–۶۵۱). Falak ol-Aflak castle is amongst the most important structures built during the Sassanid era. It has been known by a number of names since it was built over 1800 years ago. The Khorram Abad River passes the eastern and south-western side of the Falak-ol-Aflak hill providing the fortress with an element of natural protection. Today, the western and northern sides of the hill are bordered by the residential districts of Khorram Abad. The foundations of the castle measure approximately 300 meters by 400 meters. The height of the entire structure, including the hill, reaches to 40 meters above the surrounding area. The castle itself covers an area of 5,300 square meters. This space is divided into four large halls, and their associated rooms and corridors. Originally the castle used to have 12 towers, but only 8 remain standing today.