That is not quite an illusion. The interior sits roughly one and a half to nearly two metres below the surrounding land surface, giving the whole structure the quality of a shallow basin ringed by a drystone wall. From outside, the wall barely registers, rising only around half a metre above field level in its better-preserved northern arc. Step inside, however, and the vertical depth of the construction becomes apparent, the dressed stone faces dropping cleanly on both sides of a wall nearly two metres thick.

The enclosure is roughly circular, measuring about twenty-four and a half metres north to south and twenty-five metres east to west, with a narrow gap of less than a metre in the wall at the north, which would have served as an entrance. The western half of the floor is level; the eastern half tilts gently downward toward the east. Around much of the outer perimeter the wall has deteriorated or tumbled, and heaps of field clearance stone, gathered over generations of farming, have been piled against it, blurring its original outline. Local tradition holds that the enclosure was used as a sheep pen, and the form supports that well enough: the sunken interior and substantial walling would have provided shelter from Atlantic weather as well as a secure boundary, while the hilltop position gave a clear view of the surrounding land.