The trail for this cache begins at the end of Gresham Street. Start by taking the firetrail that goes off to the right. When this trail comes to an end, take the narrow path that heads down the hill, after about 40 meters this path will branch into two. Take the right hand path down to the river. It's possible that the path to the left might take you on a more direct route to the cache, but I've never gone that way since whenever I come down here its to visit the waterhole which is to the right. The walk isn't too long, but it is quite steep, and at times the trail can fade to almost nothing. When you get to the river the waterhole will be about 10-15m to the right, if you'd rather get straight to the cache just follow the creek upstream. Once you reach GZ, the cache should be fairly easy to find.
There is some optional swimming at the waterhole, with three different sizes of rock jumps (small, medium, large). It's been a long time since I've jumped off any of them though, and the underwater terrain could have changed a lot since then, so always check for submerged objects and jump at your own risk. Also don't pindrop, the water isn't that deep, and even without pindropping you'll probably hit the bottom. In hindsight this is probably a pretty dangerous place to go rock jumping, so I'll just cover myself by saying "Don't jump off any rocks" (but if you want to do it anyway it's a lot of fun).
The real challenge of this cache will be opening it to gain access to the log book. Closing it should be easier, but can still be quite tricky. Have a good try at closing it enough so that it fits into its protective outer casing, if this isn't possible just jumble it up enough so that it will still be a challenge for the next finder, and leave a message in the logs, so that I can come and fix it. The cache will still be able to hold up to the elements pretty well even without its outer casing, so don't feel bad if you can't get it back in, and have to leave it out. This should all make sense when you find it.