What makes Dunbell Big unusual is not simply that it no longer exists, but that it was excavated just before its destruction, leaving a detailed record of something the landscape has otherwise swallowed whole. A 1967 aerial photograph had already caught its outline, a sub-circular shape defined by a fosse, the term for a rock-cut or earthen ditch, pressed into the eastern tip of that ridge above the Nore valley.

When excavated in 1972, the enclosure proved to have an overall diameter of 56 metres, larger than the roughly 40 metres suggested by the earlier map. Its defining feature was a V-shaped fosse cut directly into bedrock, some five metres wide and two metres deep, with no accompanying bank. Curiously, the ditch appeared to have been deliberately backfilled with loosely packed stones at some point in its history. Amongst the material recovered were a fragment of an amber bead, a piece of a lignite bangle, and a hone stone used for sharpening blades. Inside the levelled interior, excavators found patches of intensely burnt red earth, the remains of post-holes arranged in two intersecting arcs, a possible hearth, and several pits. The excavator, Foley, proposed an early medieval date, partly on the strength of these finds and partly because of the enclosure's close resemblance to a ringfort, the familiar circular farmstead of early medieval Ireland, located roughly 290 metres to the north-west and itself previously excavated. Two further monuments once stood nearby, another enclosure about 200 metres to the north-east, also lost to quarrying, and a ringfort roughly 220 metres to the north-north-east that still survives. Whatever community occupied this ridge, they left traces across a surprisingly compact area of ground, most of which the stone industry has since taken back.