It sits about five metres from the entrance causeway, and nobody is entirely certain what it was for. The possibility that it is associated with the fort is noted but unresolved, which gives the whole site a slightly open-ended quality that more famous monuments rarely manage.

The fort itself is a subcircular rath, the most common type of enclosed settlement in early medieval Ireland, typically built between roughly 500 and 1000 AD as a farmstead enclosure for a single family and their livestock. At Ballynaclogh the enclosure measures approximately 39.4 metres east to west and 34.7 metres north to south, sitting on an east-facing slope in grassland. A rath of this kind is defined by an earthen bank, and often by an external fosse, which is simply a surrounding ditch dug to provide material for the bank and to add a further barrier. Here the fosse survives along the south-south-west through west to north-north-west arc, meaning it is best preserved on the sheltered, western side. The entrance causeway on the west, where the fosse is bridged to allow access, is still legible on the ground. The site is described as being in fair condition, which in the context of Irish field monuments usually means it has survived farming and time without serious collapse, though equally without any restoration.