Happincraig Plantation is between Hunterston A Power Station and the Three Sisters cliffs. This wooded area hides a cave. It is located behind the old pumping station, shown bottom middle of image.
This cave would have been used by many people over the years, possible to hide goods or to hide from people trying to kill them. It has been hidden away for many years and the only way you would know it was there would be to look at old maps or to read this website.