Festungsfront Oder-Warthe-Bogen

The Festungsfront Oder-Warthe-Bogen, also called the Festung im Oder-Warthe-Bogen or Ostwall, and in Polish the Międzyrzecki Rejon Umocniony, MRU, was a fortified military defence line of Nazi Germany between the Oder and Warta rivers, near Międzyrzecz. The part around Międzyrzecz has been colloquially referred to as the Regenwurmlager. Built in 1934–44, it was the most technologically advanced fortification system of Nazi Germany, and remains one of the largest and the most interesting systems of this type in the world today. It consists of around 100 concrete defence structures partially interconnected by a network of tunnels. Some of the forts and tunnels are available for visiting.

The most interesting part is the central section, which begins in the south with the so-called Boryszyn Loop near the village of Boryszyn and extends about 12 km to the north. Another interesting part of MRU is located in Pniewo in the Międzyrzecz District.