Alum Mountain is a pretty awesome piece of geology. It's been used for mining alunite (hydrated aluminium potassium sulfate), with the remains of those mining operations scattered about the mountain, but alongside the track near the top are a couple of impressive gravity-defying pinnacles.
There's limited parking on the eastern side of the Alum Mountain Trail bridge over the Pacific Highway (waypoint P0), otherwise you can park on the western side and walk across. From the trailhead T0, follow the Boolah-Dillah track up and around and then continue north along the mountain walking track from the Worimi Cultural Area. After passing below a high vertical cliff, you'll come to the first pinnacle (R0) and then some fifty metres further on, the second one where the cache is hidden.
Once level with the second pinnacle, look for a narrow path down to the saddle. GPS reception at GZ is not ideal due to the vertical rock faces close by, so the hint is fairly explicit to take you from there. The cache page's background image might also prove helpful. The container is a low-profile black Duratech instrument case and includes a pencil. Please make sure to rehide it completely out of sight as this location is attractive to muggles.
Congratulations to Banj5150, the first to conquer the pinnacle!