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 in Madagascar, 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.
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.