Yet Dún Ceartáin Nó Gleann An Ghad is precisely that, a promontory fort whose defenders relied less on walls than on geography. Three sides of the headland drop away into steep cliffs, the shore beneath reachable only with considerable effort. The fourth side, facing north-east back towards the mainland, required something more deliberate: a low earthen bank, 2.5 metres wide and barely half a metre high, drawn across the neck of the promontory to separate it from the surrounding pasture. A promontory fort is one of the simplest forms of prehistoric coastal fortification, using natural cliff edges as the bulk of its defences and concentrating human effort on the one landward approach. Here, that effort has worn thin. A faint depression along the outer face of the bank is the ghost of what was once a ditch, and much of the bank material itself appears to have been carted away at some point, possibly to construct a nearby field boundary of the kind built by the Land Commission during its twentieth-century programme of land redistribution in the west of Ireland.

What survives still carries detail worth reading. Several large flat stone slabs lie recumbent within the remains of the bank, suggesting it was once revetted, that is, faced with stone to hold the earthwork together and give it a more formidable appearance. A gap near the northern end of the bank may preserve the outline of an original entrance. The level interior holds traces of old cultivation ridges, the kind left by lazy-bed potato farming, but these are cut across by three long, shallow hollows ranging from five to seven metres in length, scattered without apparent order. Similar hollows appear in the adjoining fields, and their presence after the cultivation ridges places them in a later period. They may be the remains of kelp-kilns or kelp-stacks, features associated with the seaweed-burning industry that was significant along the west coast of Ireland from the seventeenth century onwards, producing an alkali used in glass and soap manufacture. The combination of prehistoric earthwork, post-medieval ridge cultivation, and possible kelp-processing gives this small headland an unexpectedly layered biography.

The site sits within open pasture, and the freshwater stream running through the adjoining field is a useful landmark. The cliffs that define the headland on three sides make the shore below essentially inaccessible, so the fort is best appreciated from the landward side, where the eroded bank and its flat stone slabs are most legible.