This is a rath, the most common type of early medieval enclosure in Ireland, typically built as a farmstead between roughly the fifth and twelfth centuries. An earthen bank would have enclosed a family's house, outbuildings, and livestock, offering a degree of status and security rather than serious military defence. What survives at Knocknagulshy is modest but legible: a roughly circular enclosure measuring around 37 metres north to south and 41 metres east to west, enclosed by an earthen bank still standing to about 1.2 metres in height.

The eastern side of the enclosure retains a shallow fosse, the external ditch that was dug when the bank was thrown up, the spoil from one forming the body of the other. On the south-eastern to south-western arc, the bank has been levelled, most likely through agricultural activity over the centuries, and the remaining bank has been topped with field clearance stone and incorporated into a modern fence line. It is a familiar story for ringforts across Ireland: gradual absorption into the working farm, the ancient boundary quietly pressed into service as a convenient field division. A survey of the Ballinrobe district and the Lough Mask and Lough Carra area, compiled by D. Lavelle in 1994, recorded the site in its current condition, which suggests the damage visible then is likely the same damage visible now.