The co-ordinates above are not for the cache, the cache can be found by completing the "North Warnborough to Greywell Canal Walk" Adventure Lab series.
You can find further detail about the smartphone app for Adventure Labs here: https://labs.geocaching.com. If you already have the app then search on nearby Adventures to find "North Warnborough to Greywell Canal Walk". The whole Adventure and this bonus cache should take you just over an hour to complete.
The coordinates for this physical cache will be revealed after you have visited and answered a question at all five locations of the Adventure Lab series. Once you have completed all sections of the Adventure, open the “View Journal” section of the Adventure and scroll right to find the coordinates.
When placed, the cache (a 35ml camo tube) contained a log book only, please bring your own writing implement.
When the inner area of the castle is closed due to a partial wall collapse please use the following formula to calculate the answer to question 2.
(The total number of upright wooden posts making up the fence around the castle * 6) + 6.