Introduction to the Dongning Fortress Group: The Dongning Fortress Group is more than 110 kilometers wide in front and more than 50 kilometers deep. Since August 1933, the Japanese army employed at least 170,000 Chinese laborers and spent more than 10 years until the end of the war. Not yet completed. The entire fortress group is divided into three floors: upper, middle and lower. It has a total of 40 military warehouses, 50 artillery positions, 76 bunkers, more than 300 underground war rooms, and more than 400 permanent fortifications, which can defend 300 mm caliber artillery bombardment.