Royal National Park (RNP) is a protected national park in New South Wales (NSW). It is just about 1 hour drive south of Sydney. It was the country’s first official national park. More information can be found at National Parks website.
There are two ways to get to RNP depending on where the starting point of the walk is.
One way is to catch a Blue Mountains train from Central station and get down at Waterfall or Helensburgh stations.
The other way is to go to Cronulla from Central station and take a ferry to Bundeena. Note: Opal cannot be used on the ferry as it is a private ferry and they only accept cash.
More details and up-to-date information can be found on NSW Transport website.