Limestone scenery is often known as karst after the Kras plateau in Slovenie. Limestone is highly prone to corrosion. Even rainwater, turned naturally into carbonic acid by dissolved carbon dioxide, is enough to etch away the rock as it trickles down through joints and bedding, Over millions of years, cavities open up in the rock, Cavern roofs may eventually collapse to create poijes (craters), natural bridges and gorges,