There are many great gravel bike tracks in Australia, and the best one for you will depend on your personal preferences and riding level. Some popular options include:

• The Bicentennial National Trail: This 5,330-kilometer (3,314-mile) trail stretches from Cooktown in Queensland to Healesville in Victoria, passing through a diverse range of landscapes including forests, deserts, and mountains. It's one of the longest and most challenging gravel bike tracks in Australia and offers a true adventure for experienced riders.
• The Munda Biddi Trail: This 1,000-kilometer (621-mile) trail runs from Perth to Albany in Western Australia and passes through some of the most beautiful and remote wilderness areas in the country. It's a challenging ride but offers a unique experience of the Australian landscape.
• The Mawson Trail: This 900-kilometer (559-mile) trail runs through the mid-north of South Australia, passing through a range of landscapes including hills, forests, and outback. It's a challenging ride with a mix of gravel roads and singletrack, and offers a great way to explore the region's history and culture.
• The Great Victorian Rail Trail: This is a flat and easy gravel bike track that runs for 134 km between Tallarook and Leagan Gull in Victoria. It's a great option for families or riders looking for a more leisurely ride.
• The Brisbane Valley Rail Trail: This 161-kilometer (100-mile) trail runs from Wulkuraka to Yarraman in Queensland, and it's a great option for riders looking for a mix of gravel and sealed roads, as well as great scenery.

Ultimately, the best gravel bike track in Australia will depend on your personal preferences and riding level. It's a good idea to research different tracks and talk to local riders to find a trail that suits your needs.