Established around 1945
This military facility was constructed in order to protect Altteureu Airfield, an important military strongpoint. There are 13 cave fortifications near the foot of Songaksan Mountain, and the tunnel and entrances take centipede-form. 1,433m long, this is the 2nd largest tunnel fortification found in Jejudo Island. It also has 43 entrances, which is the largest number of entrances in Jejudo Island. It serves as a witness of Japan’s history of invasion, showing how Japan used Jejudo Island as its base of resistance against its enemies in late phase of the Pacific War.