A wooden boardwalk hugs the top of the bluff at Twelve Apostles. The walkway provides spectacular and ever-changing panoramic views of the rock formations jutting from the sea. In case you are counting, you will only see eight stacks. Five have succumbed to the relentless waves of the Southern Ocean. Geologists believe the lifespan of a stack – starting as a cliff, evolving into a column and then crumbling – is about 600 years.