hollgrotten caves (hollgrotten caves), hell-grotto or tropfsteinhoehlen hoellgrotten baar (hollgrotten baar)

adventure ancient art attraction background black cave cavern caves caving clip dark darkness deep design drawing earth entrance formation geology glowing graphic green ground hole landscape light limestone mountain natural nature night outdoor outside rock scene scenery stalactite stalactites stalagmite stalagmites stone tourism tourist travel tunnel underground water yellow hollgrotten hell-grotto tropfsteinhoehlen hoellgrotten baar switzerland schweiz