Chalky Chinnor (Adventure Lab - Bonus)
Cache is not at the posted coordinates. You'll need to complete the accompanying Adventure Labs to work out where it is. The Adventure Labs take you on a tour of Chinnor's industrial and agricultural heritage. You will visit Chinnor Windmill, Chinnor and Princes Risborough Railway, Old Kiln Lakes Nature Reserve, and a Beehive Kiln.
After visiting each of the Adventure Lab locations and successfully answering the questions you will be given values for A-E which you simply need to enter into the below formula to work out the location of the bonus. The bonus is located about half a mile from the railway parking up a steep path.
The cache can be found at: N 51° 41.ABC' W 0° 53.DE3'
Note: I struggled to get a good GPS signal at GZ so have provided a generous hint and spoiler photo.
Congratulations to Team Hippo for the FTF!