Should visitors be charged to access natural sites?

In Victoria, there's a push to charge a fee to view the iconic Twelve Apostles on the Great Ocean Road.

Around the country, some of our national parks are free, but you pay to visit the most popular, like Kakadu. Nearly all of our beaches are free... but you'll get often slugged for parking.

So, what's reasonable when it comes to charging access to Australia's great natural wonders?