This spot is not far from GZ for a well-known, but sadly archived, cache - The Eastern Come In Sucker. This cache is nothing like it, it just shares a similar space although at a different elevation. I've passed this point so many times, I even used to see rock climbers here on either side of this great cutting, but I never knew how you could get to GZ.
The Comenarra Parkway was built in the late 60s-early 70s back when they used to just smash roads through bushland and national parks. There was a road here formerly which was slightly south of here. The Island was created when the new route was drilled through just north of the old route.
I've rated this a terrain 4 just to make people aware of the hazards near GZ. The reality is you will either approach via a terrain 2 route or a terrain 5 route if you have the right equipment. I'd recommend the easy way.
To find the cache you don't need to go near any edges and I wouldn't recommend this for younger children at all.
Enjoy the unique perspective at GZ.