This oval earthwork measures roughly 45 metres north to south and 40 metres east to west, surrounded by what remains of an earthen bank. Though time and farming have taken their toll, you can still make out the defensive structure; the bank stands about three-quarters of a metre high on the inside and half a metre on the outside, with its best-preserved section along the northern edge. The eastern side has been incorporated into a hedgerow, whilst the western and southern portions have been largely levelled over the centuries.

What makes this site particularly interesting is the presence of an outer enclosure that wraps around the main ringwork, creating what archaeologists describe as an irregular bailey. This secondary defensive space varies considerably in width; it extends about 45 metres from the main enclosure on the southern, western, and northern sides, but narrows to just 8 metres on the east. The boundary of this outer area is marked by a scarp roughly 0.8 metres high, though a hedgerow has obliterated part of it in the southwest section.

Ringwork castles like this one represent an important phase of Anglo-Norman fortification in Ireland, typically dating from the late 12th or early 13th century. Rather than the more famous motte-and-bailey design with its characteristic mound, ringworks relied on circular or oval banks and ditches for defence. The Coolkill example shares similarities with another site at Harsemead in County Wexford, suggesting these fortifications followed recognisable patterns across the region. Though no outer fosse (defensive ditch) is visible today, the surviving earthworks offer a tangible link to the medieval landscape of North Tipperary.