Because I lived in Shuolong Town, the place where I lived was the entrance of the underground Great Wall, so I entered and visited. This is the late 1970s, the underground fortifications built in the Vietnamese self-defense counterattack, the wartime facilities are relatively complete, command, communications, hospitals, ammunition depots... The year I went, there were few tourists, walking alone in the dim light. Here, you can imagine the tragic war of the year, imagine the bravery and perseverance of the military who defended the country.