Guardian Unlimited | Special reports | Last secrets of Nazi terror - an underground labour camp

Trawl through Stasi archives stumbles across records of hidden horrors and hidden treasures As a small boy growing up during the second world war, Dieter Michaelis knew to keep away from the old salt mine. The only hint of what was going on inside came when prisoners wearing blue-striped uniforms arrived under SS guard to collect bread from the bakery. "We were told they were bad people. They were enemies of Germany. They had to be locked up," Mr Michaelis, 68, said. "We didn't talk about it at school." It was here in Wansleben am See that one of the last secrets of the Nazis was hidden. Now, 60 years after the war, documents found in the archive of East Germany's secret police, the Stasi, reveal how the Nazis used a vast subterranean complex as a concentration camp. A retired pit foreman Horst Bringezu stumbled on evidence while researching a local history of the mining industry. Documents revealed that some 1,500 prisoners worked among its vaults; many died. They also revealed that the SS had used the secret tunnels linking two mine shafts to store rare books, priceless paintings and letters by Goethe - all now vanished. In 1944 the SS picked 300 workers from other camps, including Buchenwald 75 miles away, to hack out vast underground chambers. Out of reach of allied bombers, production equipment was lowered into the mine. Deep underground, the Polish, French and Russian workers - some Jewish - assembled parts for Germany's war industry.