This story presupposes firstly that there ever was this amount of gold, then that the gold was collected and put onto a train, and finally that it stayed on the train and that this is the train.
The German Nazi regime was, right from the start, quite incredibly bad at running an economy quite apart from Hitler's staggering ineptitude at pretty much everything he tried. The regime invaded and looted places mostly to try to prop up their own failing economy; much of their gold was sold, often to the Swiss, to give them the currency they needed to keep a dysfunctional wreck of an economy moving. Towards the end of the war the Nazis were essentially utterly skint, and the idea that they had tonnes of gold to move about is laughable. Even more laughable is the idea that this would be moved in the direction that the Red Army would be invading from.
If gold was going to be going anywhere, it would be onto a plane and off to Argentina where a host of assorted war criminals hid for the remainder of their lives; it would not be heading straight into the hands of Joe Stalin and his manky mates.
No, this is likely a bog-standard armoured train, with the bog-standard weaponry aboard. So, some machine guns front and rear, a couple of 88mm anti-aircraft guns, plus some anti-tank ammo (88mms worked great for either task) plus cargo space. Goodness knows what was in the cargo space; men, ammunition, fuel; who knows.
Then you come to the problem of digging all of this out. It is a pretty safe bet that there'll be some explosives in the train, but until you have a look, you don't know how much. The problem with going and having a look is that you might find out how much the fatal way. Then there's the fact that this is probably going to be a war grave; you don't know if people died on the train when it got sealed in, or if there are the graves of slave workers in the tunnel complex. All in all, a difficult problem and one I'd leave well enough alone.