pedestrian-road tunnels by reservoir lake gigerwaldsee gigerwald lake / unesco world heritage tectonic arena

abandoned arena background black cave cavern coal construction copper corridor dark dig energy engineering entrance excavate explore geology gigerwald gigerwaldsee gold hard heritage historical indoor industrial industry inside interior iron lake light machinery metal mine mineral old path pedestrianroad pit railroad reservoir rock safety sardona schweiz shaft silver spooky stone switzerland tectonic tektonikarena tool tunnel tunneling tunnels underground underpass unesco unescowelterbe way work world