The unexpected legacy of Hitler's hidden Nazi tunnels
In western Poland, beneath the hills and the forests, lies a forgotten network of underground tunnels and fortifications originally built as a defensive line for Nazi Germany. It was once part of the most technologically advanced fortification system of Nazi Germany, but now has an altogether different purpose.
Forming part of the Nietoperek Nature Reserve, the tunnels have become the largest hibernation site for bats in Northern Europe.
Video by Michał Białożej