The underground system features a unique 'system of blockhouses' connected by tunnels reaching depths of up to 40 meters.
Over 12 species of bats hibernate here annually, making it one of the largest bat reserves in Europe.
The tunnels include abandoned train stations and specialized technical rooms once used by the German military.
The complex was never fully completed or tested in a large-scale offensive, as the front line bypassed it rapidly in 1945.
Portions of the underground were used for testing weapons and high-secret military research during World War II.
Some tunnels were purposefully flooded to protect the facility and hinder enemy advancement.
The Międzyrzecki Rejon Umocniony (MRU) is a massive German fortification system built in Western Poland between 1934 and 1944. The Pniewo site serves as the central museum and entry point to the underground network of bunkers, combat shelters, and interconnecting tunnels. Spanning approximately 32 kilometers, this defense line was designed to protect the Third Reich's eastern border. The facility functions simultaneously as a military museum and a protected winter habitat for over 30,000 bats. Visitors can explore various route lengths, including sections that navigate through original concrete corridors preserved in their mid-century state. The site is notable for its 'dragon's teeth' anti-tank obstacles still visible in the surrounding landscape. Subterranean temperatures remain constant throughout the year, independent of surface weather conditions.
The exterior 'dragon's teeth' anti-tank obstacles and the heavy steel armored cupolas at the Pniewo entrance.
Wear sturdy, waterproof hiking boots as floors are uneven and often damp.
Bring a heavy jacket, as the underground temperature remains near 10°C regardless of the season.
Book guided tour slots in advance during peak summer months to ensure underground access.
Attempting to explore the massive fortification system without a guide, as the network is vast and lacks navigation signage.
The underground tunnels are partially closed to tourists during peak bat hibernation months to minimize disturbance.
Strict silence is required in hibernating areas to protect the bat colonies; do not use flash photography near bats.
