The earthworks of a coastal promontory fort sit on a broad headland amid ordinary-looking pasture and tillage, their banks so reduced by time that they leave no trace at ground level. This is a site that exists, in practical terms, only from the air.

A promontory fort is among the older types of Irish defended enclosure, typically formed by cutting off the neck of a headland with one or more banks and ditches, allowing the sea to do the work of defending the remaining sides. At Doonmore, two banks and a counterscarp bank, the counterscarp being an outer defensive rampart facing away from the enclosed area, run for about 40 metres in a straight line across the western part of the headland, enclosing a roughly rectangular area of around 50 by 70 metres. Their existence was confirmed and photographed by Markus Casey during an aerial survey in 1999. Sea rocks extending some 40 metres out from the headland suggest the landmass itself may once have been considerably larger, meaning the original fort could have occupied more ground than what survives today. A towerhouse, Dromore Castle, was subsequently built on the same headland, visible from some distance, indicating that this elevated, sea-facing position was considered worth occupying across more than one period. A pier now sits immediately to the northeast of the castle, adding a further layer to the headland's long use.

Because the remains are invisible from the ground, there is nothing conventionally to see at the site itself. What the place offers instead is a kind of quiet calibration: standing on unremarkable grass above Doonbeg Bay, knowing that the faint geometry of an ancient enclosure lies somewhere beneath your feet, detectable only to someone looking down from above.