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. In the central section the bunkers are interconnected with an underground system of tunnels, 32 kilometres long and up to 40 metres deep. In the underground system there are also railway stations, workshops, engine rooms and barracks. It is also the largest European underground bats refuge, giving shelter to some 32,000 bats of 12 species in the wintertime.