The Výpustek cave is unique, not so much for its natural features, but more so for its man made interventions. It is a huge tunnel-like, Y-shaped passage, once believed to be the largest cave in Moravia. As the cave was long and broad and was easily accessed by road, it was readily exploited by people, with uses ranging from a source of fertiliser (bat guano and phosphate clay) to an underground weapons factory – the Germans installed concrete floors and electricity during the Second World War, allowing them to assemble airplanes safely underground.