The 1935 Ordnance Survey six-inch map marks it simply as "Souterrain", a souterrain being an underground stone-lined passage typically associated with early medieval settlement, used for storage or refuge. But what survives above ground tells a slightly different story: a roughly circular area, measuring about 5.8 metres north to south and 7.3 metres east to west, enclosed by an earth and stone bank standing 1.3 metres high. The interior sits slightly below ground level, giving the whole structure the appearance of a hollowed mound rather than the entrance to a subterranean passage.

Within that interior lie four large prostrate stones, ranging from 0.48 metres to 1.2 metres in length, scattered across the depressed ground. A single upright stone, 0.88 metres tall, faces the bank to the north. Whether these stones are remnants of an earlier structure, displaced elements of a collapsed feature, or something else entirely is not recorded. What adds a further layer of interest is the site's situation: it lies approximately 70 metres north of the Coom river, and directly across the water stands a ringfort. The pairing of an earthwork and a ringfort on opposite banks of a river, oriented to face one another, is the kind of spatial relationship that tends to suggest deliberate organisation of a landscape rather than coincidence, though what connected these two features, and when, remains open.