All Nations Park is built on the site of the Northcote Brickworks, which operated from 1866 to 1977. Check out the photo in the gallery from 1977 showing the size of the hole they dug. After the brickworks closed, the quarry was used as a council tip until 1998. When I first placed this cache, I asked what these spiky cog things were. Thanks to the other finders, I can report that they are more properly called sheepsfoot rollers or padfoot rollers (thanks jammalees), lambsfoot rollers (thanks ewashereandthere), or pigfoot rollers (thanks n0w0rries): suffice it to say that the rollers are said to have 'feet' of some kind or another. You don't have to call them anything - just enjoy the cogs as industrial art or as a climbing wall.
The cache is a nano but should not be hard to find, apart from the muggles who inconsiderately walk up to the plaza or walk dogs around the park. GZ is near the gates of a carpark, so the cache is readily accessible to all ages. Some times of year there is a mulch mountain here in the carpark too.
Longer time cachers might recognise this as the site of iamapom's "Big Knobbly Roller Thingos " (2011-2012) and "Big Knobbly Roller Thingos Again" (2013-2015).