This is a physical cache which you can find after completing the Melksham Art Trail Adventure Lab. There is nothing at the posted coordinates apart from a place to park if you are feeling energetic.
You can find further details about the App for Adventure Labs here: https://labs.geocaching.com/
The whole Adventure Lab and the bonus cache should take you less than an hour to complete by car.
Direct link to the Adventure Lab is here https://labs.geocaching.com/goto/melksham