Falak ol Aflak Fortress one of the most impressive fortresses in Iran, is among the most important structures built during the Sassanid era (226-651 A.D). It has been known by a number of names such as Shapur-Khast or Sabr-Khast fortress,Dezbaz, Khoramabad castle, and ultimately the Falak ol Aflak Castle. 
It is situated on the top of a large hill within the city of Khorramabad, Lorestan province. The Khoramabad River runs past 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 Khorramabad. The foundation base of the castle is 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. It is 2,860 meters in perimeter and its tallest wall is 22.5 meters high. When originally built the castle used to have 12 towers, but only 8 remain standing today. The materials used in the construction of the fortress are mud-bricks, mud-fired bricks, stone, wood, and mortar. The Sassanid engineers have equipped the castle with a dehumidifier system which is one of the wonders of the ancient world. Currently, The castle is managed by the Iran Cultural Heritage Organisation. At present, there is an Anthropology museum inside the castle, showing Lorestan's cultural elements.