Adolf Hitler’s huge abandoned tunnels in European country - still not fully explored

The tunnels are located in Poland's Owl Mountains. (Image: Getty)

Adolf Hitler's genocidal regime built a huge mysterious complex of tunnels outside Germany that remain to this day - and some parts of it are yet to be explored. The project, codenamed "Riese" (or "Giant" in German), was built between 1943 and 1945, and saw a series of fortified tunnels being dug out underneath Ksiaz Castle and the Owl mountains that surround it, in the Polish town of Walbrzych.

The project was abandoned due to various factors, not least the advance of Allied forces as the final days of Hitler's rule over Germany approached. A total of 5.5 miles of tunnels across seven subterranean complexes were completed, though it's not entirely clear what the purpose of the vast site was.

Zdzisław Łazanowski, a guide at the City of Osówka told The Sun: "Our best idea is that it was meant to be the headquarters of the army... and also the headquarters for the main person in the Third Reich - Adolf Hitler."

5.5 miles of tunnels were built, though the site was never completed. (Image: Getty)

It had been thought that a fabled Nazi 'Gold Train' could be stashed within its tunnels (Image: Getty)

But as allied forces stormed across Europe, the tunnels were turned into a weapons factory.

The tunnels are now a tourist destination, though Łazanowski told the outlet that not all the tunnels have been explored, with debris from destoyed parts of it preventing them from being reached currently.

The bunker is one of many lasting reminders of the Nazis' monstrous cruelty, having been built using slave labourers and prisoners of war.

Various equipment - that which wasn't taken by Soviet forces - can still be seen, as well as a railway built within it.

Treasure hunters had previously believed that it could be hiding a long-sought-after Nazi "Gold Train", carrying untold riches.

A train from what was Nazi-controlled Lower Silesian capital of Breslau (and Wroclaw) was said to have been loaded with treasure stolen from museums, nobles and banks and been heading to the heart of the Third Reich in 1945.

But the train then vanished without a trace, so the legend goes, with many believing the treasures are out there somewhere.

Two explorers searching for the Gold Train had previously claimed to have found it in the Riese site, though what had appeared on radar images to be a buried train was later revealed to be merely a rock formation.

Historians have cast doubt on the existence of the train, with no evidence of it found to date.