Secret tunnels found under Szczecin’s Ducal Castle leave historians baffled

The surprising find was made after expert cavers began exploring a network of passages that had been constructed during WWII. Zamek Książąt Pomorskich w Szczecinie/PAP

Dating from mediaeval times, researchers have discovered two secret tunnels running underneath the Ducal Castle in the northern city of Szczecin.

The surprising find was made late last week after expert cavers began exploring a network of Nazi-era passages that had been constructed during WWII.

It was whilst investigating the cause of an accident that researchers came across the German tunnel built by the Nazis.Zamek Książąt Pomorskich w Szczecinie/Facebook

Built in 1346, but copiously remodelled in the years after, the castle was formerly the seat of the Dukes that ruled the Duchy of Pomerania until 1637.

In later years, Catherine Opalińska, the Queen of Poland, lived here, as too did the future Catherine II of Russia who was born and raised within the castle’s walls.

The researchers then discovered the medieval tunnels. Historians, though, have been left baffled by the mediaeval fragment, the existence of which has never been knowingly recorded up until now.  Zamek Książąt Pomorskich w Szczecinie/Facebook

Suffering 60 percent destruction during both Allied air raids and the Red Army’s westward sweep, the castle was rebuilt between 1958 and 1980 primarily because of its significance to Polish and Slavic history.

In 2017 the castle again found itself flirting with trouble, this time after a pillar in the north wing collapsed and brought down a section of the ceiling.

Posting the find on Facebook, the castle said: “Fragments of underground medieval corridors have been discovered next to the previously known tunnels from World War II.”Zamek Książąt Pomorskich w Szczecinie/Facebook

It was whilst investigating the cause of this accident that researchers deduced the presence of a German tunnel similar to the ones found across the city.

Together with ambitions to renovate the castle’s terrace, this original reconnaissance spurred castle authorities to conduct a thorough examination of the entire hill.

Zamek Książąt Pomorskich w Szczecinie/Facebook

Built in 1346, but copiously remodelled in the years after, the castle was formerly the seat of the Dukes that ruled the Duchy of Pomerania until 1637.Zamek Książąt Pomorskich w Szczecinie/Facebook

Commissioning a professional team of cavers from a Szczecin-based firm specializing in extreme working conditions, a 16-metre deep vertical shaft was drilled into the castle’s core before exploration could begin.

When it did, the caving unit found the Nazi tunnel – which branched in different directions – in good condition. However, as they walked deeper they also discovered the prefabricated concrete giving way to a 25-metre stretch of vaulted brickwork.  

Speaking at a press conference, the castle’s director, Barbara Igielska, said that these bricks have now been authenticated as dating from centuries previous: “After conducting an initial investigation into the wartime tunnel we learned that it was 270-metres in total length.

Two soldiers of the German Wehrmacht take a stroll along the riverfront in what was then called Stettin.Bundesarchiv, Bild 101II-MN-1572-15A / Mendel / CC-BY-SA 3.0

“At one point though, the reinforced concrete turns into bricks and mortar. Having sent samples of these elements for analysis, we can confirm that they are from mediaeval times.”

Concerns have now been raised about the safety of the tunnels and just what else might lie below the surface.

Karol Krempa, head of the castle’s renovation and investment department warned that further work would be vital to both our understanding and safeguarding the castle.

Suffering 60 percent destruction during both Allied air raids and the Red Army’s westward sweep, the castle was rebuilt between 1958 and 1980 primarily because of its significance to Polish and Slavic history.PAP

“This initial exploration demonstrates that we’re dealing with a far more complex situation than we first imagined,” he said.

He added: “These tunnels create a runoff for groundwater so urgent intervention is needed… What we can say is that there are a lot of sinkholes in these tunnels but we don’t know if they are the result of anthropogenic activity or if they are natural.

“We need an expert opinion. We also can’t rule out that there might be much more to the 270-metre section of tunnel than we are currently aware of.”  

The castle’s director, Barbara Igielska, said that the bricks have been authenticated as dating from centuries previous: “After conducting an initial investigation into the wartime tunnel we learned that it was 270-metres in total length.Marcin Bielecki/PAP

Measuring between 2 and 2.3 metres in height, further issues may arise in the coming weeks once mining robots are called in to carve a path through to the entrance.

“We’re concerned how the mediaeval part will react to changes to the humidity once the entrance is opened,” Igielska said.

But whilst ensuring the stability of the castle promises its own complex set of challenges, even more mystifying is the purpose of the tunnels.

The race is now on to prevent the tunnels from further damage caused by water.Zamek Książąt Pomorskich w Szczecinie/Facebook

The Nazi stretch would most likely have fulfilled shelter and storage use. Historians, though, have been left baffled by the mediaeval fragment, the existence of which has never been knowingly recorded up until now.  

What is apparent is an ultimate ambition to make these discoveries accessible to the public.

Igielska said: “We care about these tunnels. We have no intention to fill them with concrete or destroy them. While we need to fill the voids around the tunnels, we would like to make the tunnels available to visitors in the future.”