Kazdere/Gazidere, a tributary of Gökirmak, cuts the rock that the Boyabat Castle is perched on with a dramatic pair of vertical walls. The wall on the castle side has a window on the rock face illuminating descending tunnels to a newly discovered large underground city from Roman times. The tunnels may also have served for water supply and safe passage during siege.[2]
The castle, which probably has not been in serious use since around 1300 A.D. but may be as old as 2800 years, overlooks the Gökırmak valley. This valley is long and lies parallel with the Black Sea coast. Together with the similarly placed Yeşilırmak (river) valley further east, it forms a natural east–west pathway used since the antiquity as a trade route, possibly as part of the silk road. The castle may have served to protect this trade route. Being a suitable distance from Durağan, Hanönü and Taşköprü, it may have provided safe stop for caravans.
