Deli owner Yang Guoqing was camping by the Great Wall in 2008 when he discovered relics from the Battle of Nankou, a largely forgotten conflict during the Second Sino-Japanese War that claimed more than 20,000 lives. He has used his metal detector to recover more than 3,000 military relics, which are displayed in his makeshift basement museum. Mr. Yang seeks to educate future generations about the cost of war and value of peace, particularly amid growing modern tension between China and Japan.