NOTE the cache is not on the walls, it is external to them.
Morgan’s Mount was constructed in 1645 during the siege of Chester in the Civil War as an observation platform and gun emplacement. After the Battle of Rowton Heath in September of that year, a gun on the Mount was destroyed by Parliamentary forces. It was originally named the Raised Square Platform, and is said to have been named later after the Royalist Captain William Morgan, or his son, Edward.
At the base of the tower is a life size sculpture representing the civil war cannon destroyed. This is where you will find the cache