Engineers are set to start surveying a railway embankment in south-western Poland to establish how to dig out a “gold train” that is thought to have been buried there in the dying days of the Third Reich.

The existence of a Nazi gold train, its whereabouts and its cargo — possibly stolen valuables and artworks — remain one of the great unsolved mysteries of the second world war.

“In the past 70 years, three cold war secret services — the United States, the Russian, then the Polish — carried out searches,” said Piotr Koper, a 44-year-old builder who claims to have found the suspected armoured train with a fellow treasure hunter. “We succeeded because we are local people.”

Some historians believe up to three trains laden with arms, art, gold and archives vanished in a 18 sq mile area near the present Czech border as the Red Army advanced in 1945. The strategic area includes Hitler’s command post at the grandiose Ksiaz Castle (formerly known as Fürstenstein) and Project Riese, a suspected secret weapons programme.

Read the article “Poland’s Nazi Gold Train: Are Investigators Closing in on One of WWII’s Greatest Unsolved Mysteries?” on theguardian.com.