The Great Mosque, located within the old city texture of Ereğli, was built by Mehmet Bey, the son of Karamanoğlu İbrahim Bey, in 1426 as a foundation work. Built of rubble stone, the mosque has a rectangular plan. The harim part of the building is divided into pitches perpendicular to the mihrab wall with thirty-two columns. Some of the column capitals of the harim part are spolia. The harim part is covered with a wooden rounded flat ceiling from the inside and a hipped roof from the outside. The minaret of the building, which was also used as a watchtower in its time, is dated to the Anatolian Seljuk Sultan Mesut I period, 1116. There are tile ornamentation details on the cylindrical minaret body built of cut stone material.