Skip-the-line available The Książ Castle Underground and Project Riese
What the tunnels beneath the castle are, who dug them, and how to visit with the history in view
Beneath Książ Castle runs part of one of the most sobering sites in Lower Silesia: unfinished tunnels driven into the rock by Nazi Germany under the codename 'Riese' between 1943 and 1945. This is a real and difficult chapter of wartime history, built by forced and concentration-camp labour, and it deserves to be understood with that gravity before you visit. Here is what the tunnels are, what happened here, and how the guided Underground Tourist Route works today.
What Project Riese was
'Riese' — German for 'giant' — was the codename for a vast construction project undertaken by Nazi Germany between 1943 and 1945 across Lower Silesia. It comprised several underground complexes, including works beneath and around Książ Castle itself and a cluster of much larger tunnel systems dug into the nearby Owl Mountains, at sites now known by names such as Osówka, Włodarz and Rzeczka.
The project's exact purpose was never officially documented and remains debated by historians: evidence suggests the castle was being adapted as a headquarters or official residence, while the mountain complexes were intended as underground factory space, sheltered from Allied bombing. What is certain is that the scale of ambition far outran what the project ever achieved — historians estimate only a small fraction of the planned tunnelling was completed, and only a modest share of that was ever reinforced with concrete, largely because the extremely hard rock of the region made drilling far slower than planned.
The people who built it
Project Riese was not built by free labour. Construction depended on forced labourers, prisoners of war, and — from 1944 — concentration camp prisoners, many transferred from Auschwitz, including large numbers of Hungarian, Polish and Greek Jews. Camps were established near the work sites to house them, including one adjacent to Książ Castle itself, and conditions were brutal: historians estimate thousands of the prisoners forced to work on Riese died from disease, malnutrition, exhaustion, dangerous tunnelling conditions and mistreatment by guards.
This history is the reason the Underground Tourist Route is presented, and should be understood, as a memorial and historical site rather than simply an atmospheric attraction. The guided tour addresses this context directly, and visitors are encouraged to approach the tunnels with the same seriousness given to other Second World War sites in Poland.
Why the tunnels were never finished
As Soviet forces advanced into Lower Silesia in early 1945, work on Project Riese was abandoned unfinished, camps were evacuated, and the remaining prisoners were liberated as the war ended. What is left beneath Książ and in the Owl Mountains today is exactly what the name suggests it might have become and never did — a fragment of an enormous, unrealised undertaking, its purpose still not fully settled by historians.
That unfinished, raw quality is part of what makes the site so striking to visit: bare rock passages, incomplete chambers and the sense of a project stopped mid-motion, rather than a polished museum reconstruction.
Visiting the Underground Tourist Route
The guided Underground Tourist Route takes small groups through the section of tunnels beneath the castle on a fixed timed slot, with a guide explaining the history as you go. Access involves a descent of several dozen metres, mostly by stairs, so a reasonable level of mobility is needed, and — for safety reasons — very young children are not permitted on the route.
The air underground stays cool year-round, so bring a warm layer whatever the season, and wear flat, comfortable shoes rather than anything with a heel, since the surfaces are uneven and can be damp. Because group sizes are limited and the route runs on fixed slots, it is the one part of a Książ visit that reliably sells out on busy summer days — booking your preferred time ahead is the only way to be sure of it.
Frequently asked
Was the underground finished?
No. Like the rest of Project Riese, the tunnels under and around Książ were abandoned unfinished as the war ended in 1945. That raw, incomplete state is much of what makes them so striking to walk today.
Do I need to book the underground in advance?
In summer, yes. The route runs on timed slots for small groups and the popular afternoon walks sell out days ahead. We reserve the slot you want at checkout.
What was Project Riese actually for?
Historians still debate the full purpose. The evidence points to the castle being prepared as a headquarters or residence, with the much larger Owl Mountains complexes intended as underground factory space sheltered from bombing — but no single official explanation survives.
Who built the tunnels?
Forced labourers, prisoners of war and, from 1944, concentration camp prisoners — including many Hungarian, Polish and Greek Jews transferred largely from Auschwitz. Conditions were severe, and a significant number of prisoners died during construction. The site is presented with that history in view.
Is the visit appropriate for children?
Older children generally find it fascinating rather than frightening, and the guided format keeps the pace manageable. For safety reasons very young children cannot enter the underground area, and the history is presented honestly rather than sensationalised, which is worth knowing before you bring a family.