Sitting on a gentle rise in open pasture in County Sligo, this roughly circular enclosure measures 31 metres east to west and 35 metres north to south, its interior raised above the surrounding ground. The whole thing is defined by a layered set of earthworks: a substantial inner bank of earth and stone, a fosse (a defensive ditch, typically dug to reinforce the bank above it), and then an outer bank beyond that. The original entrance survives too, readable in the landscape as a four-metre gap through the inner bank, a causeway crossing the fosse, and a corresponding eight-metre opening in the outer bank, all aligned to the east-south-east.

Ringforts, known in Irish as raths when earthen rather than stone-built, are among the most common archaeological monuments in Ireland, most dating to the early medieval period, roughly the fifth to twelfth centuries. They functioned primarily as enclosed farmsteads, the banks and ditches marking out a family's territory and providing some protection for livestock. At Sheeanmore, the layered defence of inner bank, fosse, and outer bank suggests a site of some status, since simpler ringforts typically made do with a single bank. Two linear quarries on the south-east side of the enclosure, one at the inner foot of the internal bank and one cut into the base of the fosse, indicate where material was extracted during construction. A later drystone field wall, running east to west, now bisects the interior into two equal halves, a reminder that the site has continued to be used, and altered, by successive generations of farmers long after its original function was forgotten. Perhaps most intriguing is the souterrain, an underground stone-lined passage or chamber used for storage or refuge, whose remains extend from the inner face of the western bank into the interior. Such passages are frequently found in association with ringforts across Ireland, though their full extent at Sheeanmore has not been fully mapped above ground.