Miedzyrzecki rejon umocnień-MRU (bunkers in Poland created by hitler between 1934–1944) part 2/2

The Międzyrzecz Region is one of the largest underworld fortifications in the world. The underground section of the central MRU is now a bat reserve, where winter over 30,000. individuals belonging to 12 species of bats. The total length of underground corridors is estimated at 32-35 km