This cache is at the Glenrowan Rest Stop.
Unfortunately, it is just signposted as "Glenrowan", so if you weren't sure where you were, and wanted to turn off to Glenrowan, it would be slightly confusing. (not to mention annoying!)
Luckily, you can pretend you just turned off to grab the cache.
The real turn off to Glenrowan is about 6 km down the highway.