5 /5 Elena Arena: Gorgeous. I did the segment of the Great North Walk from Hornsby Heights to Cowan. 20.75 km; elevation gain 800m; total time 8h49 (moving time 7h52)
The route starts on McKay Rd with a fire trail easy to follow but then it meets the Great North throughout an unmarked path (it is signaled by little towers of rocks) so keep an eye on your app.
Km 3-9 are mainly flat and run along the Berowra Creek, really beautiful.
After that youll find a bit of moderate up and down (eg about 150m), take your time it might be slippery.
The last part (from Berowra Waters to Cowan) is the most "wild", moderate difficulty but practicable by everyone.
The Great North is pretty well maintained and clear to follow but I recommend using a map (Google doesn’t have the full route) to be sure of staying on the right trail.
First facilities (toilets, drinking water, as well as shelters, bins and bbq) after 6km, at Crosslands Reserve (accessible by car). Other toilets at km12 in Berowra Waters. Flush toilet at Ridge Top Campground but not drinking water (to the person who left the bottled water there: THANK YOU!). Toilets and drinking water at Cowan station.
Did it on October 6th and did not meet any leaches.