They call it "Rhizome"? You've got to be kidding! ANd they call that ART? Oh, Fore! Crying Out Loud!...
A rhizome is really a collection of roots. I'll leave that analogy there. (I love a bit of controversy!)
The artwork near the posted coordinates cost approximately $750000, if the website is to be believed. Again I say, "Fore! Crying Out Loud!"
So - this is a simple one. Drive, walk or ride anywhere near it and determine how many bits of it stick up higher than the nearest light pole. (Don't get caught out with parallax error though.)
Take this single digit number as "R" (for rhizome) To get to the cache, use S35 13.(4+R)38 E149 07.(2+R)10 From GZ you can see the structure clearly, and there is a space for a car park (if you're observant), but please use caution as there are plenty of mtbikeroz types around. 
FTF: SecretSquirrel-BJC