Known in Irish as An Dún Rua, this promontory fort on the Dingle Peninsula sits at the foot of Mount Brandon, wedged between two narrow sea inlets, Coosatna and Coosavuddig (the latter better known as Brandon Creek). On its landward side, the promontory is cut off by a natural trough running between the two inlets: twenty metres wide and an estimated ten to fifteen metres deep. That alone would have made the place extraordinarily difficult to approach. Whoever built here recognised the trough as a ready-made defensive line and simply added to it, running a stone wall along its upper edge to close off the gap.

The antiquarian Thomas Westropp visited in 1910 and recorded the wall extending for over 120 metres, describing it as twelve to fifteen feet thick and high. What survives today is considerably less. The wall appears to have been constructed as two drystone revetments, each face built of stacked unmortared stone, separated by a five-metre-wide ledge or berm, with the outer revetment rising around two metres and the inner up to three. Much of it has since collapsed into an unfaced scarp, a rubble slope that has lost any dressed surface it once had. The entrance passage, cutting at right angles through the defences for about thirteen metres, has also changed markedly. Westropp measured its external width at just 1.6 metres; today that opening has widened to nearly ten metres, suggesting significant disturbance in the intervening century. Only two or three of the upright stone slabs that once lined the entrance passage remain in place. A turf track running up to peat cuttings on the summit likely accounts for some of the missing stonework, the wall cannibalised over generations for more immediate practical purposes. Inside the fort, a sub-circular enclosure that Westropp identified at the south-western corner is still visible, a low bank of grass-covered earth, peat, and transversely-set stones, measuring roughly 42 by 36 metres, with a possible entrance on the north-east side marked by two upright slabs set less than a metre apart. A sheep-shelter or turf-shed of more recent date occupies the eastern end of its southern wall, a reminder that these ancient enclosures have rarely been left entirely to the past.