Nothing beats getting out in the bush in Sydney. This cache is not all that far out unlike its sister cache Hawkesbury Lookdown Book Exchange. This has simpler road access and a somewhat shorter, although steeper, walk.
Park at the end of Calabash Road (which comes off Bay Road) just at the start of the Waddell Ridge Fire Trail (see coords). The trail heads down the hill past the gate into the bush and it goes down... and down... You will come to a junction where the fire trail goes up the hill but the track goes down to the right. Take the trail to the right - they both go to the same place but the track is flatter. Look at the shaped stones along the edge of the track here. What were they for?
The track rejoins the trail and heads along fairly level terrain until it starts to go up again. At this point take the faint track to the right (see waypoint). This track is overgrown but gets better. It is also lined with stone blocks in places and looks like it was once well used. You are heading all the way down to answer the question in the cache name. You can follow this track all the way to Berowra Creek.
Before you look for the cache head to the end of the track and have a look at the cave and the track down to the water. Some big fish in the water here. Head up the hill to GZ to find the cache. I placed it away from the cave as I think it is a site of Aboriginal significance. The track itself probably predates European settlement but looks like it was enhanced by settlers. Enjoy the views from the cave and GZ. Now you've got the walk back up! From the water's edge you'll climb over 200m back to the car but it only took me 32 minutes and I'm no triathlete. Enjoy the books - I made another book exchange rather than fill the ammo can with more plastic junk. Have a read or swap.
Note if you have a small boat you may save yourself a walk!