The bunker system incorporates a series of 'dragon's teeth' anti-tank obstacles on the surface.
The tunnels feature specialized rooms for ventilation, water filtration, and electrical generation.
The complex remains a protected wintering ground for several species of bats, with populations reaching tens of thousands.
The underground temperature remains constant at approximately 10 degrees Celsius year-round.
The facility was intended to connect with the Oder-Warthe-Bogen defensive line to protect the eastern German border.
Portions of the underground system have been intentionally flooded or blocked to prevent unauthorized access.
Evidence of post-war testing of explosives is visible in certain areas of the concrete fortifications.
Pętla Boryszyńska is a central segment of the Międzyrzecki Rejon Umocniony (MRU), a massive Nazi German defensive line built in the 1930s in Western Poland. The site features an extensive underground tunnel network connecting hardened bunkers, known as Panzerwerk, designed for infantry and artillery defense. Visitors navigate approximately 2 to 3 kilometers of subterranean corridors located 30 to 50 meters below the surface. These tunnels include remnants of underground railway tracks, reinforced blast doors, and original engineering installations. The facility was designed to withstand heavy shelling and function as an autonomous fortress for extended periods. It serves as one of the largest bat hibernation sites in Central Europe, influencing site access during winter months. The structure represents a significant example of 20th-century military fortification engineering and logistical planning.
The entrance portal of the primary Pz.W. 717 bunker showing the exterior fortifications and steel armor plating.
Bring a warm jacket and sturdy, non-slip footwear, as the tunnels are consistently cool and damp.
Carry a headlamp or high-powered flashlight, even if a guide is present, to see the ceiling details.
Allow extra time for the transition between the warm surface temperature and the cold underground climate.
Do not attempt to explore unguided or peripheral tunnels, as the ventilation and structural integrity are not maintained outside of official tour routes.
Tours are significantly restricted or suspended from mid-autumn to early spring to protect hibernating bat populations.
Maintain silence to protect bat colonies and follow all marked safety paths to avoid unstable subterranean zones.
