It is also called Osoksan Fort as it is located in Mt Osok in Ryonggang County, Nampho City.

This stone fort is 6620 meters in circumference and its height is 4-5 meters in hilly district and 10 meters in flatland.

There are 2877 battlements and four bastions in its front and right and left sides.

The fort has four gates in all directions, and there was rich source of water inside the fort at that time. Various pond and well sites can be seen there.

Four general's terraces installed on peaks in the north, east, west and south of the fort were used as command posts in wartime and observation posts in peacetime.

The fort was repaired by the Koryo Kingdom in 919.

The fort shows high fortification skill of the Korean nation.