Through The Quayhole
We hope you are enjoying your time in our wonderful city.
You're looking for a disguised micro/small cache.
Looking over the Mersey you can see the wirral peninsula and behind lies Brunswick dock. The dock was opened in1832, specifically for importing timber. It consisted of two lock entrances from the river. In 1854, Cato, Miller & Company built ships at Brunswick Dock. The dock was rebuilt with a southern extension in 1905. The dock closed in 1975, although one lock was reopened in 1987 for small watercraft.
We believe the structure at GZ is the top part of the old lock gate from the entrance to the dock here.
This is located in a very high muggle zone, so please be discreet and use care when retrieving and replacing this cache as it is homemade and not easily replaced.
Special, magnetic tool required. We have placed one for you to find or use your own.
Please note exactly where you find the cache and replace where found, otherwise the cache likely will jam for the next finder. Thank you. 
Enjoy.