You are looking for a tiny black cylindrical cache at the top centre of the Cayley Embankment.
The co-ordinates will bring you to GZ which is the tree opposite the shelter with the blue roof which is on the promenade below. ***EDIT The shelter has now been removed. You can now only see the small paved area marking where it stood.***
***EDIT The tree has been cut down and is now a stump!
Your own pen and tweezers are a necessity.
Due to many DNFs, I feel I must now add; sit down alongside the tree and admire the view! This is a tricky one so please don't submit a maintenance request when you can't find it ;)