We toured a 32 km network of tunnels that led to multiple bunker sites, we were not able to walk all of the tunnels but we still got to walk quite some distance in them with our guide. They were built by the Germans but not used in the war for battle. In the area, there were ~100 fortified structures, numerous hydro-technical buildings, and anti-tank barriers designed to protect access to the firing positions. It was fascinating to learn about how thick the steel turrets were on top of the bunkers and how the bunker sites would work together on protecting one another.