While going through the historic chapters about Nazi Germany domination, it can be seen that between 1943 and 1945 fortified tunnels near the Polish town of Walbrzych were built by labourers and prisoners of the war.
In western Poland, Germans built tactical tunnels to reinforce the eastern border and strength of the defence. It was once a part of the advanced fortification system but now it is used for a completely different purpose
It should be mentioned that these never completed tunnels were supposed to be Hitler's new headquarters, while some experts claimed that these could be used as the weapon factory. Some of these tunnels are currently open as a tourist destination.
Who is using this mysterious construction?
The construction of the Ostwall (East Wall) started in the spring of 1936 and due to a budget-related issue, the work was brought to a halt in 1938. Over the time the tunnel was abandoned. But now, the Nazi tunnel is now helping the wildlife to thrive, especially to one particular species.
An expert from Vincent Wildlife Trust, Henry Schofield said that Ostwall is now the largest hibernation site for the bats in northern Europe. The site is manmade and artificial located in an area which is geological and doesn't have any underground structures so it became a very important resource for the bats in this area.
Scientists and volunteers from across Europe, gathered at the Nietoperek Nature Reserve to conduct annual bat census every year. The counting begins early in the morning and researchers enter the mysterious tunnel before daybreak.
In a BBC video, John Haddow, a conservation consultant stated that inside the 32-kilometre tunnel, "if you are walking through the north of the underground is one and a half, two hours walk, just to get to the beginning of the counting section," which is split into nine.
Researchers reveal that when the census takes place it causes disturbances among the bats and awakes some of these species from hibernation. So the aim of these researchers is to keep the disturbances to a minimum. In this Nazi tunnel, the inhabitants, the bats can be spotted on the walls, ceiling, crevices, pipes and alcoves.
There are some dangerous loops in the middle of the tunnel floor which could cause danger because the team concentrated on counting and during the process, there is a chance of falling down if they miss one hazard which was used as a drainage system during the Nazi era.
Why bats are going to hibernation in the tunnel?
As per Schofield, early in the year, bats can feed on insects but during the winter those insects disappeared from the location. So the bats have adapted to this annual cycle by going into hibernation and during the process, the whole body process slows down.
In terms of hibernation, bats need consistently low temperature and high humidity. For the bats, the best location inside the tunnel is the second level which is located in the middle of the other two levels.
It should be noted that every year, at least 35,000 of 12 bat species spend winter months hibernating in the underground tunnels which were constructed over 80 years ago for the purpose of war.