The white froth in the distance indicates the shaft is open to the sea; I received the impression it's possible to get in from the beach at low tide, though the workings themselves are well below sea level and visitors' habit of dropping stones down (myself included) could be a problem. While we were there, a family arrived with carrier bags of rocks, specifically for dropping.

Even on an overcast January afternoon, daylight outside meant my eyes couldn't adjust to the darkness of the shaft; I could just about make out the froth with the naked eye, but I saw the side shafts at the top and right of the image for the first time when I downloaded the camera. It was lucky that the image is even vaguely in focus.