At the place known locally as Spinkadoon, on the northern Mullet peninsula in County Mayo, this ancient logic plays out on a particularly uncompromising piece of ground. The cliffs here fall vertically to the Atlantic, and the boggy, uneven terrain inland gives the site a quality of deliberate isolation. The headland stretches roughly 150 metres and widens to 70 metres at its broadest point, but it pinches down to just 10.5 metres at the neck, which is precisely where the builders concentrated their effort.

Two parallel earthen banks, each about 1.5 metres wide and half a metre high, run straight across that narrow neck, set 6 metres apart. To the east of them, faint traces of a wide shallow fosse, a defensive ditch, are still legible in the ground. Further west, some 26 metres into the headland, the remains of a more substantial collapsed wall, 1.6 metres wide, mark what was once a third line of defence, though it has now nearly entirely fallen. No original entrance survives; the gaps that cross the banks today were opened by sheep rather than by any ancient design. The interior is rough ground, scattered with rock outcrop and loose boulders, and a rectangular hollow that has been dug there in relatively recent times sits just inside the ruined wall. The site was first noted by Brown in the 1890s and given a brief description by the antiquary Thomas Johnson Westropp in 1912, placing it within a long tradition of scholarly interest in Ireland's coastal promontory forts, though it has never attracted much wider attention. To the south, another fortified promontory and two hut sites are visible, suggesting this stretch of the Mullet once supported a small but organised community making use of its dramatic, sea-girt terrain.