During the Japanese colonial period, Penshan had nine mine tunnels, with the underground passages intersecting with each other and forming a network of more than 600 kilometers of tunnels.
日治時期本山共有 9 條坑道，地下坑道縱橫交錯，長達六百多公里；「本山五坑」是純金礦坑道，也是現存唯一可通行的坑道。