Li River Cruise
Karst landscapes form when carbonate rock - such as limestone, calcium carbonate - is dissolved by rainwater and groundwater. Carbon dioxide in the water produces a weak carbonic acid, which dissolves the rock. This creates limestone caves all over the world. What makes Guilin different, accounting for the peaks seen here, is that enormous underground sinkholes, caused by the process mentioned above, have merged and collapsed over geological time to produce the Li River valley; Guilin's rounded and gently eroded peaks are leftovers from this collapse. Eventually, they too will disappear.
Other karst landscapes, although none so spectacular, are found in Kunming (Stone Forest), Thailand, and Viet Nam.