A promontory fort is a type of prehistoric enclosure in which a natural landform does much of the defensive work; here, a single bank and ditch cut off the only easy approach from the south, effectively turning the headland into a walled space without the need for encircling ramparts. The bank, running 43 metres across the neck of the promontory, survives to about 1.2 metres in height and holds its form well on the eastern side, though it flattens and spreads where the ground drops away to the west. The external ditch, still measurable at over eight metres wide, runs alongside it.

The structure itself may be remarkable enough, but the ground beneath it has added further layers of interest. Geophysical survey carried out under licence in 2003, reported by Cooney in 2009, identified two ring barrows, a form of circular burial monument, on the outer side of the bank, one of them faintly visible as a surface feature. Circular structures were also detected within the enclosed area. A later survey, conducted by The Discovery Programme as part of the Lambay Island Archaeological Research Investigation (LIARI) project under licence in 2012 and reported by Dowling in 2014, confirmed those internal anomalies. What this suggests is a site with a longer and more layered history than a single defensive bank might imply, with burial and possibly other activity both predating and accompanying the fort's use. Natural sandstone outcrops along the northern edge of the headland, and a landing place at the north-eastern end would have made the site accessible from the sea.

Lambay Island lies roughly five kilometres off the north County Dublin coast, near Rush, and is privately owned. Access is not open to the general public in the normal way, and any visit requires prior arrangement. The fort sits at Scotch Point in the north-western corner of the island, where the views across to the mainland coast are extensive. The earthwork is subtle rather than dramatic, so patience and a good eye are rewarded more than urgency; the eastern section of the bank, being better preserved, is the clearest place to read the structure. The presence of the ring barrows just outside the bank, one of them traceable as a slight surface undulation, gives a sense of how long this particular piece of headland has drawn human attention.