And what about under the earth? 'Karst' originated as the name of a limestone region in Slovenia but the word now has a wider meaning: terrain with special landforms and drainage characteristics resulting from the solubility of the local rock.
All rocks dissolve to at least some extent in natural waters (which are often slightly acidic), but some rocks are more soluble than others. Limestone, dolomite and other rocks made mainly of carbonate minerals are the most easily dissolved. In landscapes formed of carbonate rocks, solution is an important part of the weathering and erosion processes that have shaped the land over thousands and millions of years.
The dissolving and removal of the bedrock helps to create the well-known karst landforms, such as rock towers, natural arches, sinkholes and underground caves and rivers. The cavernous, 'Swiss cheese' landscape means that nearly all drainage is underground, and surface water is scarce. Karst landscapes are amongst the most spectacular and unusual on Earth - and endlessly fascinating to scientists and visitors alike.
Within the Greater Blue Mountains World Heritage Area, Jenolan Caves are the most well known example of karst. The caves with their amazing and beautiful formations are the big attraction, but just as interesting are the surface karst features. Jenolan has blind valleys and sinkholes, the narrow grooves in surface rock called rillenkarren and several fine natural arches.
Despite being packed into quite a small area of limestone, Jenolan has one of the most extensive cave systems on the Australian mainland. Recent research has shown that one reason for the complexity of the caves is that they have been forming here for an exceptionally long time - about 350 million years. Jenolan is one of the oldest known cave systems in the world.
There are seven other small areas of limestone karst in the Greater Blue Mountains World Heritage Area, as well as Wombeyan Caves right next door, and Abercrombie Caves to the west. And karst processes are not restricted to limestone. Solution has played a role in shaping some of the sandstone formations too, notably the intriguing domes and towers known as 'pagodas'.
Karst and cave systems have prompted a number of milestones in the conservation story of the Greater Blue Mountains, from the visionary protection of Wombeyan Caves in 1865 to the historic dispute over limestone mining at Colong in the 1960s.