Close to Kamenica hill, 14km away from Niš, the inconspicuous entrance to Cerje cave is tucked away near the spot where the Provalijska river sinks into the earth, 515 meters above sea level. The cave is hydrologically active, geologists estimating that it originated over 2 million years ago. The end of the cave remains undiscovered. Cerje is beset with cave formations throughout its length. It's a wonderful underground world of mysterious corridors and vast halls on average 15 to 40 metres high, showing hundreds of hydrologically formed stalactites, stalagmites, cave corals and crystal flowers - of dramatically different sizes, shapes and colours. Something called helictites, found here, represent a special kind of cave jewellery which, contrary to all laws of physics and gravity, extend in all directions like electrified hair.  In 1998, the Institute for the Protection of Natural Monuments proclaimed Cerjanska Cave a first category natural treasure. However, due to the lack of funds, it is still not open to visitors - a fact that will hopefully change, on the condition that it isn't given over to the damaging thralls of mass tourism.