Agrabit Cistern. It is a special device made by Arabs to collect water in the desert. To visit the Agrabit Cistern, you need to climb the castle and overlook the cistern. The cistern is divided into two pools, the small one is used to collect rainwater, and the large one is used to precipitate impurities to form clean water. Because Kairouan is a water-scarce area, the locals built 15 cisterns in 862 AD, which is a symbol of the wisdom of the people living in the desert.