It's part of the Porongorup National Park, in between the Stirling Ranges and Albany. There are a couple more hikes in the area that we planned on doing but decided to save ourselves because of the plan to climb Bluff Knoll the next day. The Castle Rock hike isn't especially hard in the type of terrain, it's just all climb which some might find a struggle.
The other reason it is a grade 4 hike, is that at the end, you have to climb up over a few giant boulders, and then up a narrow ladder that takes you onto the granite skywalk. It's not for the faint of heart, but it does offer fantastic views of the area. I have been up there in light rain though and that can be unpleasant.
Being a sucker for a good view, if you are ever in Porongorup and yearn for more, pop over to Mount Barker and head on up to the Rotary Lookout, for impressive views of all the peaks in the area, plus the giant TV transmission tower.
Drone Panorama (excuse the horrendous HDR)
The rotary lookout in Mount Barker
