Complex Riese in JugowiceA worker at the site of a newly discovered armored door of the former Complex Riese in Jugowice , Lower Silesia , Poland , 02 July 2016 . The complex is one of seven underground structures that were part of the Project Riese - a mining and construction project of Nazi Germany . The construction project started in the Owl Mountains in 1943 and was never completed . Tunnels and chambers were driven into the mountain slopes and the entire project consisted of a network of road , rail , water , sewage , telephone and energy infrastructures . The construction work was done by forced laborers and prisoners of concentration camps . The purpose of the project remains unclear to this day . EPA / ALEKSANDER KOZMINSKI POLAND OUT EPA / ALEKSANDER KOZMINSKI POLAND OUT ▶ [ 핫 클릭 ] " 쿠란 경구 못 외 면 고문 " 방 글 라 인질극 생존자 증언 ▶ [ 핫 클릭 ] 광현 호 살인 피의자 , 선장 · 기관장 에 23 차례 칼 휘둘러 ▶ [ 통통 영상 ] 출근길 강남대로 한복 판서 ' 무 자비 폭행 '< 저작권자 ( c ) 연합뉴스 , 무단 전재 - 재 배포 금지 >