These tunnels are 12,000 years old and stretch from Scotland to Turkey!
They are impressive!
According to some experts, these tunnels were used as roads - for a secure journey that doesn't depend on wars, wild animals or climate.
Other theory is that these are the gates to hell...
Dr. Henry Kusch, a German archeologist, has been studying these tunnels for many years and even wrote a book called "Secrets of an underground door to the ancient world". The scientists says that the extension of these tunnels is unprecedented!
"In Bavaria, Germany, we've found around 700 km of tunnels. In Styria, Austria, - 350 m. There are many of tunnels underneath Europe."
Some of the passage ways are as narrow as 70 cm. There are rooms and spacious halls.
In the book Dr. Henry states that he has found several underground chapels.