Nobody had ever seen them open, or at least not within living memory. That detail, recorded by the antiquarian Thomas Johnson Westropp in the early twentieth century, points almost certainly to a souterrain, an underground stone-lined passage or chamber, typically built during the early medieval period for storage or as a place of refuge. What makes the site at Dunganville Upper quietly compelling is not just this buried rumour of hidden rooms, but the way the whole structure sits at the lip of the steep-sided valley of the River Daar, its earthworks shaped partly by the natural drop of the land, and partly by the hands of people who worked in earth and stone long before the surrounding fields were put to grass.

Westropp documented the site in his 1916 to 1917 survey, and his plan, published as plate IV of that work, remains a key record. The roughly circular enclosure measures approximately 69 metres north to south and 67 metres east to west, a substantial rath, the Irish term for a ringfort built from earthen banks rather than stone. The bank on the north-north-east to south arc is considerable, standing about 2.7 metres on the interior face and nearly 5 metres on the exterior. To the south and west, the steep natural incline of the valley effectively takes over the defensive role. A deep external fosse, a dry ditch running west to south, once reinforced the whole arrangement, though it is now almost entirely obscured by overgrowth. By the time the Ordnance Survey captured the site on their 1923 six-inch map, an outer bank was still visible to the west and east; that feature has since been removed and replaced by a farm trackway.

Access is through working farmland, so the usual courtesies apply. The most visually legible part of the monument is the substantial bank running from the north-north-east around to the south, where the earthwork is best preserved and most readable as a structure. The gap in the bank on the west side is recent in origin, filled with dumped material to form a rough causeway nearly nine metres wide, so the original entrance was elsewhere. The fosse below the bank on the western and southern sides is largely hidden under dense vegetation, which can make the full dimensions of the earthwork difficult to appreciate without moving around the outer edge carefully. The L-shaped rise in the north-east interior, low and indistinct now, is the feature most worth pausing over, even if what lies beneath it remains, as it apparently always has, a matter of local belief rather than confirmed record.