Karst is a type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves, springs, and other characteristic features. Karst is associated with soluble rock types such as limestone, marble, and gypsum. In general, a typical karst landscape forms when much of the water falling on the surface interacts with and enters the subsurface through cracks, fractures, and holes that have been dissolved into the bedrock. After traveling underground, sometimes for long distances, this water is then discharged from springs, many of which are cave entrances.
Limestone is a type of carbonate rock — that is, a rock made up primarily of a carbonate mineral which, in the case of limestone, is usually calcite or aragonite. These are both forms of calcium carbonate (CaCO3). Over time, limestone may be dissolved by carbonic acid (i.e., carbon dioxide dissolved in water). Carbonic acid is formed when rain picks up CO2 as it falls through the atmosphere. Once it hits the ground, it may pick up more CO2 in the soil, turning into a weak carbonic acid solution. When this solution seeps into limestone bedrock via cracks and fissures, larger openings are created. Over the course of thousands of years, this erosive process creates underground drainage systems and caves.
Mammoth Cave,USA is the longest Cave system in the world.
Xiaozhai Tiankeng,China Largest Sinkhole.
Other examples,Yutacan peninsula,Mexico
Cockpit Country,Jamaica etc.
In India karst topography is present in the Vindhya region (mainly southwestern Bihar), the Himalayas (parts of Jammu & Kashmir, Robert Cave, Sahasradhara, the eastern Himalayas, areas near Dehradun), Pachmarhi in Madhya Pradesh, the surrounding coast near Vishakhapatnam, and Bastar in Chhattisgarh.