Boyabat Castle - Sinop Late Roman and Early Byzantine Period artifacts are exhibited and the structure is an Ottoman fortress. This situation shows that the castle was used from the Late Roman Period to the Ottoman Period. With its current situation, the city walls and bastions and construction materials clearly show that it is an Ottoman castle. However, the foundations of the castle have been laid before. Therefore, it is possible to examine the castle in two parts as the old and the new castle. The foundations of the old fortress were built in the early 6th century BC during the time of the Paflagonians. It is possible to come across Roman and Byzantine artifacts on the old foundations of the castle and on some of the inner walls of the castle. It is certain that the present castle of the new castle was built during the time of Osmanoğulları. However, due to the lack of an inscription on the castle, its construction date is unknown.
Boyabat Castle is located on one of two steep rocky hills in the Gökırmak Valley where Boyabat district is located. The castle was built in accordance with the natural structure of the rocks. Some of the towers between the castle bodies are made of rectangular and some of them are rounded and there are stairs leading up to the towers. Entrance to the castle is through a small gate next to the large round tower from the southeast corner.