Silesia was beyond the range of our bombers for much of the war and the Germans located a lot of factories there, some in tunnels.
As the Russians advanced on Silesia Hitler declared the capital, Breslau, a "fortress" city, meaning the Germans would allow it to be surrounded and would fight it out to the end to slow the Russian advance. Hitler was a military genius, doncha know.
Anyhow, needless to say there were large scale and paniced evacuations in advance of the Russians. So, someone might have concealed a tunnel. But a gold train? The Nazis always got their loot out first. Hard to believe they would have left much behind. Our guys found several trains full of loot and they had been taken as far from the Russian front as the Germans could get.
Playing “hide the tunnel” was commonplace in occupied countries... ;’)