Well, as the article says it is a local legend, but not an entirely unsubstantiated one.

The Nazis tended to plunder and loot art and other valuables basically everywhere they went. At the beginning of the Third Reich, Hitler came up with the idea for his Führer Museum in Linz. They wanted to fill it with treasures of the Great Masters, basically showing the superiority of the Germanic people. Art was looted basically everywhere the Nazis went (at first they only took over museums but then that turned into stealing people's personal possessions pretty quickly). In addition to the museum, Hitler and other high ranking nazi officials wanted art for their personal collections. They didn't exclusively loot art, basically anything of value was stolen (gold, jewels, books, etc). there was actually a special task force, the Einsatzstab Reichsleiter Rosenberg (ERR) dedicated to the looting.

As the war's destruction became parent, groups of American and British curators and art historians formed a group called the MFAA, short for Monuments, Fine Arts, and Archives. You may know of them from the film "Monuments Men". They were on the front lines of the war, looking for art and helping to preserve whatever they found (they also often helped preserve buildings and architecture that was damaged from the war). The Nazis had caches of loot in salt mines, castles, underground tunnels. As the Third Reich fell, they destroyed many of these caches, but the MFAA attempted to find and save any art they could. In the Bernterode Mine they found the coffin of Frederick the Great, along with many other priceless pieces.

The MFAA kept working until 1946 but they still continued their efforts to encourage preservation of cultural goods, a policy that the US usually (and that's kind of a big usually but I'll get within the 20 year limit if I start on this) tries to uphold today. There are many pieces still unaccounted for, but those could have been destroyed, stolen, sold on the black market or maybe they're still out there.

So not crazy that there might be a train full of Nazi gold in a mine. Happened fairly often. I didn't see the movie so I can't speak to how good it was, but there are a bunch of books about the MFAA. Momuments Men- Robert Edsel and Salt mines and castles: The discovery and restitution of looted European art by Thomas Howe are good places to start.

I'm sorry that I can't help answer your question, but as a follow up question:

For the longest time I've been interested in the stories of Yamashita's gold. Basically it's the same thing, but referring to the gold caches that Japanese forces hid in mountains in the Phillipines. I'd love to hear a historians perspective on the validity of these stories.

The City of Walbrzych has held a conference today confirming that the train is "within the city's administrative limits", but obviously they can't say where exactly. They are informing the relevant ministries(Ministry of Culture, most likely), to take it from there. That is very impressive indeed, because the train was thought to be a legend for half a century.