The perfect place for such an experience is Jerusalem Bay located in Ku-ring-gai Chase National Park. The walk to Jerusalem Bay is perfect for those who are looking for a picturesque bushwalk without too much of a challenge.
To access the track you park at Cowan railway station and then walk across the tracks. Once you cross the pedestrian bridge which crosses the highway the walk begins and you can make your way down to the Bay.
The walk itself has one of the most iconic views along the Great North Walk, and takes you from Cowan Railway Station, down to the water at Jerusalem Bay. The walk takes you through a variety of environments, with the terrain being quite dry and rocky at the beginning and becomes more rainforest-like the closer you get to the water.
The entire walk only takes around 2 hours and is 4.9 kms, however you'll want time to go for a swim once you get down to the Bay. The waterway is part of Cowan Creek and if you go down on a weekend you will most likely see plenty of people on boats enjoying the water. The area is perfect for swimming with most of it being shallow. If you were feeling inclined you could also pack a picnic or take along a small BBQ and make an afternoon of it. Just be aware however that there are limited areas for such activities.
If you're after something a bit different make the short drive up North and experience what nature in Sydney has to offer.