25 km catacombs. Once these were silver mines, then they began to be used for household needs. In 1996, archaeologists worked in the catacombs, who recorded that the sound of an organ was heard in the place indicated by the legends, and in one of the passages, the researchers found a “luminous staircase” that emitted a reddish light. Archaeologists were examined – mass hallucinations are excluded. The reasons for the mysterious phenomena are unknown.