The tunnel, which was about high by wide, extended more than beyond the Military Demarcation Line (MDL) into South Korea. The tunnel was reinforced with concrete slabs and had electric power and lighting. There were weapons storage and sleeping areas. A narrow gauge railway with carts had also been installed. Estimates based on the tunnel's size, suggest it would have allowed approximately 2,000 KPA soldiers (one regiment) to pass through it per hour.