This is a promontory fort, a type of enclosure that exploits natural geography rather than fighting it. Where a coastal or lakeside promontory narrows, a builder need only construct a barrier across the neck to enclose the jutting land on three sides with water. The result here is an oval area roughly 68 metres by 48 metres, defended on the landward side by a wide, shallow, flat-bottomed fosse, which is essentially a ditch, with a slight bank running along its inner edge. The lake itself does the rest of the work.

What makes this particular site quietly interesting is the gap between its apparent simplicity and its long documentary history. It appears on the Ordnance Survey six-inch map of 1837 as an arc of a bank enclosing a roughly oval promontory, and on the OS Fair Plan it is explicitly annotated as a fort. By the revised 1913 edition of the 25-inch OS map, the bank is recorded as slightly more linear in character, suggesting either gradual change or a more careful survey. When the monument was described in detail in 1970, the investigators found no trace of any formal entrance, which raises questions that no one has yet answered about how the space was accessed. There is a natural rise inside the enclosure at the outer edge of the north-western quadrant, and a small, steep-sided rectangular platform near the north-eastern scarp that the surveyors noted looks conspicuously like a golf tee, a reminder that the modern world has a way of leaving its own modest marks on ancient ground. Lady's Island, a low feature in the lough, sits some 370 metres to the west, visible from the fort's interior across the water.