The karst limestone, after surface rock has weathered away, makes a ground surface which is almost imposssibly difficult for humans. Velebit in Croatia
From a World Heritage Site
, the Tsingy de Bemaraha
Strict Nature Reserve. Gradual erosion has produced vast fields of limestone spires known locally as tsingy, interspersed with dry forests, lakes and mangrove
swamps inhabited by numerous endemic and threatened lemur
and bird species.
Karst is a geological system of rocks where water has eroded (dissolved) the bedrock. If very extensive, karst can be a geographical or topographical feature.
Almost always, karst is formed in carbonate rocks, such as limestone or dolomite. Since carbonate sedimentary rocks are very common, karst areas occur all over the world.
Many karst regions display distinctive surface features, with sinkholes being the most common. However, karst surface features may be absent where the soluble rock is mantled (covered), such as by a non-soluble rock strata on top of the carbonate strata. Some karst regions include thousands of caves, and the water is generally underground.