Heciz Castle was located in the interior of Bithynia northeast of Constantinople. It is around 10 km southwest of Şile, a province on the Anatolian side of Istanbul on the Black Sea coast. The history and construction of this Byzantine castle are uncertain. As there is no evidence of any major settlement, it probably served to control a road from historic Chele (modern Şile) to the Bosphorus.

The castle is on a hill surrounded on the three sides by a meander of the Heciz Deresi stream, which is a branch of the Türknil River (historic Artanes River). The poorly-preserved castle has a polygonal plan, measuring around 150 by 60 m. A single circular tower is on the northern corner facing the narrow ridge to the north. One long straight wall runs south on the western side, leading to a well-preserved circular tower on the southwestern corner. There is another circular tower on the eastern side, while a heavily damaged square tower is on its southeastern corner. It is possible there were gates next to the circular towers on the eastern and western sides. Its masonry generally consists of large rubble stones with grayish-white mortar, though bricks can also be found in the upper sections of the southwestern tower.