The road to Ksiaz Castle feels almost too peaceful. Forested hills roll off into the distance, yew trees as far as the eye can see. And then a colossal building rears up over the landscape of Lower Silesia — dramatic and impossible to ignore.
Part Baroque palace, part Renaissance fortress, Poland’s third largest castle looks like something lifted from a fairytale, according to CNN.
But beneath the lavish architecture lies a darker story.
Here, deep in Poland’s Owl Mountains, lies a vast underground Nazi complex tied to one of the Third Reich’s most mysterious construction projects and, legend has it, a lost train filled with stolen gold.
Ksiaz’s history stretches back to the Middle Ages, when Silesian duke Bolko I the Strict built a fortress on this hilltop. Over time it expanded into a grander residence.
In 1466, Hans von Schellendorf acquired the castle and named it Schloss Fürstenstein — a title it would keep until the end of World War II.
As Lower Silesia was a part of Prussia until the 20th century, the castle became one of Germany’s most significant aristocratic residences.
In 1944, with World War II raging, the Nazis seized control of the castle from Count Hans Heinrich XVII, who had already relocated to England. Ksiaz and the Owl Mountains then became a hub for Project Riese — German for “Giant.”
The project aimed to create a network of massive underground facilities across Lower Silesia. Seven major subterranean complexes have been discovered so far, but the true purpose of the tunnels remains uncertain. Many documents were destroyed or hidden by the Nazis as the war ended.
Brutal conditions
The tunnels at Ksiaz lie away from the heart of most of the Project Riese structures, deepening the mystery here.
According to Mateusz Mykytyszyn, Ksiaz's head of public relations, it’s widely assumed this is because the castle was intended to become Adolf Hitler’s Headquarters — though definitive proof has never emerged.
What is known is the human cost.
More than 13,000 prisoners were brought to the region to excavate tunnels and construct underground infrastructure.
The tunnels beneath Ksiaz stretch nearly a mile. Some passages are constructed from reinforced concrete, made smooth and precise. Measuring five meters high, or roughly 16.5 feet, they’re wide enough to drive a car down.
Some sections are just bare rock. In one tunnel, the remains of a narrow-gauge railway used during excavation can be seen.
There are modern exhibitions here that use projections and audio to tell the story of Project Riese. Screens illuminate dark chambers with archival images and historical context. The effect is immersive and — particularly because of the human cost of creating the space they’re in — often unsettling.
Many visitors say it’s the scale that leaves the deepest impression.
Buried gold?
Despite the documented history, myths continue to swirl around Lower Silesia — especially the story of a hidden train loaded with stolen Nazi gold.
“Even today, many people are looking for the treasures and hidden tunnels here,” said Michał Miszczuk, a local guide at Underground City Osówka, another major Project Riese complex nearby.
The legend suggests that during their retreat from Wrocław — then Breslau — in 1945, Nazi forces concealed a train filled with valuables somewhere in the Owl Mountains. In 2015, treasure hunters received permission to excavate a suspected site near Wałbrzych known as Zone 65, but found nothing.
But the mystery persists, fueled by missing documents and the many undiscovered tunnels believed to remain sealed.
“Lower Silesia has been German for centuries,” explained Miszczuk. “Even if they knew the war was lost, they were sure that they would get this land back.”
Believing in a buried treasure is easier when standing in the dark tunnels of Osowka, which are rough and rocky, in contrast to the mostly smooth concrete of Ksiaz.
The complex spans roughly two kilometers, or just over a mile, with towering chambers and a 48-meter vertical shaft. Some researchers speculate that it may have been intended as a central hub connected to other Riese sites.
Today, Ksiaz Castle is one of Poland’s most popular attractions. Spring brings crowds for the Festival of Flowers and Art, while nearby hotels housed in former outbuildings accommodate visitors year-round. The castle also hosts conferences, weddings and cultural events.
The global fascination with the supposed Nazi gold train has boosted international attention.
