For more than 70 years, treasure hunters have flocked to a quiet corner of southwestern Poland in search of a legendary cache of Nazi loot. Deep inside the Owl Mountains, the Third Reich dug a vast network of mineshafts and tunnels between 1943 and 1945 (called the Riese Project), perhaps to hide a secret weapons program, or to carve out an impenetrable subterranean bunker for Hitler's last stand.
Whatever the Nazis had planned for their extensive underground complex -- dug by forced labor from nearby concentration camps -- the Soviets spoiled it. In 1945, with the Red Army at the doorstep, the Nazis fled their Owl Mountains refuge, blasting most of their tunnels to rubble behind them.
But according to legend, a Nazi freight train loaded with pillaged artwork, jewels and untold bars of gold bullion still rests somewhere beneath that rubble. Stories tell of a German miner who saw the Nazis pack up their "gold train" and park it inside the Owl Mountains, from which it never emerged.
"There is definitely a Nazi train buried somewhere in those tunnel complexes," says ecologist Rob Nelson, co-host of the Science Channel series "Secrets of the Underground," which launches its second season Saturday Oct. 28 with an episode devoted to the Nazi Gold Train.
"Having talked to the people [in Poland], and having spent time there, there's still so much that's unexplored," says Nelson, an adventurer with Indiana Jones issues. "The data says that there's only 5 percent we know about. The rest of it has been blasted away and blocked off. There's tons of stuff back there for sure."
The Nazi Gold Train story may have the whiff of myth, but it's rooted in historical precedent. A similar Nazi train carrying more than 5 tons (4.5 metric tons) of gold, 700 pounds (317 kilograms) of diamonds and pearls, 1,250 paintings and thousands of Oriental rugs -- stolen from grand estates as well as everyday victims of the Nazi genocide -- was intercepted by Allied forces in 1945 and dubbed the Hungarian Gold Train.
And the region surrounding the Owl Mountains, which was part of Nazi Germany in the 1940s, is home to several large mansions -- and one exceptional castle -- where Nazis were known to have stashed artwork and jewels. Much of it was never recovered.
The Hunt for Nazi Gold
To facilitate their search, Nelson and his co-host Stefan Burns, a geophysicist, employed ground-penetrating radar (GPR), which uses electromagnetic pulses to display a rough image of what lies beneath to a depth of about 10 feet (3 meters). They also brought along a magnetometer to measure fluctuations in the Earth's magnetic field, and a device that employs a surveying technique called electrical resistivity tomography (ERT), which can reveal underground water deposits, or more critical to tunnel-hunters, cavities and air gaps.
This isn't the first time that such technology has been deployed in search of the gold train. In 2015, teams of university researchers and amateur treasure hunters converged on the Owl Mountains region when rumors surfaced of an ex-Nazi who left deathbed instructions on how to find the train. Poland's deputy culture minister threw gas on the fire by announcing that he was "99 percent convinced" that the train had been found.
But months of scanning with ground-penetrating radar, and thermal and magnetic sensors, came up with nothing but a few subsurface anomalies.
"There may be a tunnel," Janusz Madej, head of the scientific team who searched for it in 2015, told the New York Times , "but there is no train."
Nevertheless, treasure hunters started digging in the alleged area in the summer of 2016, but after a week, they had to conclude there was neither tunnel nor train. (What appeared to be a radar image of a carriage turned out to be a natural rock formation.) But the efforts weren't a complete bust -- the town of Walbrzych did score a financial windfall courtesy of the tourists who flocked this part of southwest Poland.
Co-hosts Nelson and Burns have trained their scanners on a different location, where locals believe there's a side train track that may have connected to the main line.
"It's in a brand-new area where no one has looked before," says Nelson, who doesn't want to spoil the big reveal, but will say that they found clues to some new underground passageways, "which is huge."
One gadget the "Secrets of the Underground" crew brought with them to Poland was a handheld LIDAR scanner, which can create a real-time 3D map of any space using millions of laser points. The team used the scanner to create the first digital maps of miles of tunnel complexes that had previously only been sketched out by hand. In one tunnel, the LIDAR scanner revealed that a crack in the ceiling was much deeper than it appeared in the sparsely lit mineshaft. In fact, it led to a second level. No train, though.
"We live in a world where you feel like everybody knows everything," says Nelson, "but we still know very little about what the Nazis were doing with these tunnels. The Germans blasted them as a way to keep their secrets, and all of the plans were destroyed. That's part of the mystery."