The page co-ordinates will take you to a section of the Town Walls but NOT the bonus cache. To find the bonus cache you must complete the "Newcastle Town Walls and Blackfriars Adventure Lab" at the end of which the final bonus co-ordinates will be revealed.
The Adventure Lab cache may be found at the following URL:
https://labs.geocaching.com/goto/TownWalls
Pbeare; zntargvp.