Camp Earthworm, Regenwurmlager, Międzyrzecz, Poland

The Regenwurmlager (Camp Regenwurm, literally: Camp Earthworm) is an extensive underground fortification area constructed by Germany in 1920s-1940s, now in western Poland, near the city of Międzyrzecz (formerly Meseritz). It was a system of underground bunkers interconnected by tunnels and corridors of total length over 100 km. On the Soviet maps it was denoted as "Мезерицкий укрепрайон". In 1945 it was abandoned by the German troops retreating without significant fights.
It was a military training camp (Truppenübungsplatz) for training of fortification troops and a reserve storage and rest area. It was located by the village of Nipter (now Nietoperek) southwest of the Festungsfront Oder-Warthe-Bogen defense line and named after the nearby creek, Regenwurm. It is also close to the village of Kęszyca Leśna, where the Soviet military garrison was stationed, which investigated the area of Regenwurmlager.