This is a Bonus cache linked to the "Bamburgh: a walk through time" Lab Cache.
The cache is not at the posted coordinates.
To find the cache, you need to complete the "Bamburgh: a walk through time" Lab Cache.
The actual cache coordinates are revealed in the Lab Cache journal when you complete Location 5.
There is a path from the large car park opposite the castle (see parking coordinates) to the location of this Bonus Cache. It is a short walk of less than 300 metres. Attempting to park closer to the cache is not advised.