The bonus cache to the Adventure Lab series of the same name. The cache is not at the published coordinates which are for Arrington Gate where your adventure begins.
To get the final coordinates for this cache you will first need to complete all 5 stages of the Adventure Lab, when you have completed them you will be have both the co-ordinates for the final. (In the Adventure Lab app select view journal entries and scroll through to the fifth one to find all the information). Please leave the cache as you find it and ensure it's properly hidden again, thank you.
To complete the adventure lab series you will need to download the Adventure Lab App. This adventure can be found here: Wimpole Estate Walkabout 1
This bonus cache page has waypoints to help you stay on the right paths.