Nizwa Fort is located in the city Nizwa , about 140 km from the city Muscat . It used to be the seat of the administrative authority. The main part of the fort was constructed for 12 years. The Nizwa Fort is built in the shape of a large tower whose height is 30 m. It is anchored 30 m under the surface ,and its average diameter is 36 m. The entrance area is guarded by 2 cannons. There are 4 cannons, a part of the original equipment, still installed on the roof. Nizwa Fort is a construction with battlements, towers, secret passages and fake doors which perfectly protected access to its top. The fort had been built over an underground spring.