Most people learned to ride a bicycle when they were young and have kept the skill, if not the habit, for the rest of their lives.
Depending on the terrain, this could be a mountain bike or a more lightweight, conventional touring bicycle. These are often available to hire for a trip, along with a helmet and other safety equipment. If it’s been a while, have no fear: it will all come back to you as soon as your feet touch the pedals.
In Victoria, try ride the North East Rail Trail or The Great Victorian Rail Trail. In South Australia, the Mawson Trail is a popular route. The East Coast of Tasmania is also well-regarded. Magnetic Island in North Queensland offers a popular destination for riders.