Zahhak Castle known as Narin Castle is located on a hill in mountainous area of Sormahlu. It was first explored by a German Archaeological Panel in 1971. One of the results of exploring Zahhak Castle was discovering a great hall with side corridors and several plaster works in various designs and forms in ocher, yellow, blue and green. These designs include embossed human and animal designs, geometrical designs as well as flowers and plants. One of the main designs found in this location, is a hawk with claws on a cow's back, which is very similar to Mitra in Mithraism. Beside this design, there are other patterns like Parthian soldier, the head of several roaring lions, a goddess, and a man inside a lotus or rays of sunlight. While exploring Zahhak Castle, relics and signs of various periods including Parthian Civilization, Ashkanid Era, Sasanid Era, as well as sixth and seventh centuries A.H. were obtained.