Jenolan Caves are caves in the Blue Mountains, New South Wales, Australia; 175 kilometres west of Sydney. They are the most celebrated of several similar groups in the limestone of the country being the oldest discovered open caves in the world. They include numerous Silurian marine fossils of great interest and the calcite formations, sometimes pure white, are of extraordinary beauty. The cave network is enormous - over 40 km of multi-level passages - still undergoing active exploration.