The entire Project Riese network was constructed using forced labor from the Gross-Rosen concentration camp.
The purpose of the 'Casino' building remains unknown, though its reinforced concrete walls are several meters thick.
Underground construction techniques at Osówka utilized 'trench-cover' methods to camouflage the site from Allied aerial reconnaissance.
Geological analysis indicates the rock composition consists primarily of gneiss, which was difficult to blast and excavate.
The site features a significant amount of infrastructure designed for high-voltage electricity and ventilation systems that were never fully installed.
Despite the extensive construction, no official documentation exists specifying the exact intended use of the Osówka complex.
The tunnels include a specialized 'dam' section designed to hold back water, though it was never utilized for its intended capacity.
Underground City Osówka is the largest and most developed component of Project Riese, a secret Nazi German construction project initiated in the Owl Mountains during World War II. The site consists of a vast network of concrete-lined tunnels and multi-story surface structures whose precise original purpose remains historically disputed. Many historians speculate it was intended as a headquarters for Adolf Hitler or a secret facility for advanced weapons research. The complex includes the 'Casino' and the 'Gymnasium,' two massive concrete structures located above ground that remain in their original raw state. Visitors explore the tunnels via guided paths that highlight the unfinished chambers and massive drainage systems. The site is part of the Owl Mountains Landscape Park in Lower Silesia. The ambient temperature inside the tunnels remains constant at approximately 7 degrees Celsius throughout the year. It represents one of the most significant remnants of subterranean Nazi engineering in Europe.
The interior of the massive concrete 'Casino' building provides the most striking contrast between nature and Nazi-era brutalist architecture.
Bring a warm jacket and sturdy, non-slip footwear as the ground is perpetually damp and cold.
Choose the extreme tour route if you want to experience the flooded sections by boat or waders.
Check the official website for group size limitations during peak holiday weekends.
Do not attempt to explore the perimeter woods without a guide, as the terrain is rugged and holds hidden structural hazards.
Open year-round; often busier on weekends and during Polish public holidays.
Strictly follow the guide's safety instructions regarding restricted zones and touch-sensitive walls; do not stray from marked paths.
