The huge monolith known as Uluru - formerly Ayer's Rock - remains one of Australia's most mysterious and beautiful natural features. Rising more than 1,000 feet above the flat red center of the continent, "The Rock" is eight miles in circumference and honeycombed with caves, displaying Aboriginal wall art. Uluru once stood at the bottom of an inland ocean, and is a spectacular sight as it changes color through the day. The sandstone it is composed of contains many minerals like feldspar which reflect shades from deep red to violet, according to the angle of the sun.

However, while Uluru is probably the most famous Australian geological wonder, it is certainly not the only one. The amazing Bungle Bungles in Western Australia are huge pillars of sandstone that look like ancient ziggurats. But nature, not man, made these orange and black striped monoliths, situated in Purnululu National Park. The black stripes are caused by lichens growing on the orange sandstone. Known to Aborigines for centuries, it remained a secret to the rest of the world until the 1980s, when the stunning rock formation was spotted from the air.

The Devil's Marbles in the Northern territory are another example of Australia's geological diversity. The "marbles" are huge roughly hewn ovoid boulders piled on top of one another, some seemingly defying gravity, poised like eggs balancing on end. Made of coarse granite, the marbles have gained their shape by constant weathering.

The Great Barrier Reef is one of the few geological wonders that can be seen from space. A spectacular 161 square miles of coral reef, it stretches from New Guinea down the Queensland Coast. Dotted with coral islands, the reef is the largest structure ever built by living creatures. These tiny polyps leave their skeletal remains behind, forming stretches of coral reef.

Nullabor means, literally, no trees, and the Nullabor Plain between Adelaide in South Australia and Perth in Western Australia lives up to its name. It is a vast 155,000 mile flat desert that drops with frightening suddenness into the Great Southern Ocean. There are no towns or permanent habitations on the Nullabor Plain - and definitely no trees.

Wave Rock is a stunning formation in Western Australia that looks like a breaking wave on land. The smooth curve of the rock was believed to be caused by water erosion. Around 500 million years old, the wave shape was formed by granite flowing in molten form.

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