Going up toward the N.E of the city you will reach the Fortress also known by the locals as the Castle. It was built during the 6th century A.D. by Ioustinianos emperor on the ruins of the ancient citadel of Trikki. Afterwards it was reconstructed by the Ottomans. Nowadays it hosts the Municipal open air theatre. The Fortress is divided into three tiers. The ground tier operates as a square with a coffee bar, the second (and biggest one) has been formed into an area of rich vegetation while in its east side dominates a beautiful tall watch which can be seen from every corner of the city and was built in 1936. The third tier has a small theater in its N.W side in which many remarkable events take place. Finally, in the N.E side of the latter tier the natural steps that led to the castle walls are still preserved.
Reference : Prefectural Administration of Trikala