Two treasure hunters have started digging for a Nazi train they believe is laden with gold, despite the fact that most experts say it doesn't exist.
The train was rumoured to have been packed with treasure by the Nazis as they fled from the Red Army towards the end of the Second World War, but abandoned for unknown reasons in an underground siding that was then blocked up.
According to these stories, the train was carrying up to 300 tons of gold, as well as works of art, diamonds and weapons. The gold alone could be worth as much as £9 billion.
There's some basis for the legend: the Nazis are known to have melted down jewellery looted from Jews and other prisoners and transported as much as possible back to Germany in the latter stages of the war.
It's not impossible, in other words, that caches of treasure are indeed waiting to be found. And Piotr Koper and Andreas Richter claimed last summer to have identified one such treasure trove, nine metres underground in a railway tunnel in Walbrzych, south west Poland, by using ground-penetrating radar and other technology.
However, the pair were given permission to dig by the owners of the land, Polish State Railways, and 35 volunteers started work this morning.
The team say they expect to have completed the dig by Thursday - and one way or another, the mystery will be solved. As spokesman Andrzej Gaik tells AFP, "The train isn't a needle in a haystack. If it's there, we'll find it."
He adds: "If we find a tunnel, then that is also a success."
A tunnel, at least, is more likely. The site is known to be near a large network of tunnels built by the Nazis and rumoured to house looted treasures originally stored at nearby Ksiaz Castle.
Sometimes, treasure hunters really do find some of this Nazi gold. Last year, a team of divers discovered a ship sunk deep in the ocean and carrying £34 million worth of silver coins. Six months earlier, two bottles of 1930s Bordeaux wine hidden by the Nazis were unearthed in a network of Third Reich of tunnels near Swinoujscie in north-western Poland.
Koper and Richter plan to live-stream the excavations, here.