Gerdab Sangi is located in Takhti Square in Khorramabad, Lorestan and is made of stones and plaster. It dates back to the Sassanid era (224-651 CE) and is a circular whirlpool built for the purpose of accurate and optimal distribution of water. Encircling several springs, the edifice sits near the prehistoric Qomri Cave. The construction was once used for rationing and distributing potable and agricultural water among local population and farmers. Its surrounding cylindrical stone wall has a height of 10 meters and a diameter of 18 meters.There are a few different-sized outlets in the wall for controlling the flow of water into a canal on the west of the structure. While originally there were 7 of such outlets, however, today only one is functional. This outlet measures 160 x 90 centimeters and opens and closes like a drawer. The water flowing out of this outlet, after a path of approximately 12 kilometers, would eventually make its way to a valley called Baba Abbas. In the vicinity of this valley, and the location of the ancient city of Shapurkhast, the remnants of an old mill, which was run using water from the springs, can be observed.