Salt deposits had been mined in Wieliczka possibly as early as 3500 BC. By the Middle Ages, the mine was already providing not only a plentiful source of income, but it also became a tourist attraction. The historical chambers connected by passageways, lying at depths ranging from 64 m to 135 m, allow visitors to marvel at its natural and man-made wonders – stalactites and stalagmites, brine lakes, post-exploitation pits, former mining devices and subterranean chapels decorated with salt sculptures. The total length of the passages linking about 3000 cavities, ramps, excavation chambers and shafts exceeds 300 km, 99 percent of which is not accessible to tourists.