Karst regions often have solution caves and underground rivers.
Tips
memory
Literally 'rock-dissolving' (岩 rock + 溶 dissolve), a perfect calque for the geological process where water slowly eats limestone into towers and caves.
culture
China's most famous karst is Guilin and Yangshuo (桂林, 阳朔); the iconic peaks on the 20-RMB note are eroded karst limestone.
