Sheer drops surround it on most sides, a stream runs down the cliff face to the east, and the ground inland rises above it, meaning whoever occupied this place had the Atlantic in front of them and higher ground at their backs. What makes it worth attention is not its drama but its subtlety: the defences are almost gone. A fosse, essentially a defensive ditch cut across the narrowest point of the isthmus, and a revetted bank of earth and stone outside it, survive only as faint traces. Recent slippage along the western edge has taken more of the evidence with it.

Promontory forts, which use natural cliff edges and sea inlets to do much of the defensive work, leaving only the landward approach to be fortified with a bank and ditch, are found all along Ireland's Atlantic coastline. The site at Béal Deirg Mór sits in a landscape of hilly pastureland and sheep grazing, and it is one of three such forts along a north-facing stretch of this particular coastline, suggesting the area had genuine strategic or territorial significance at some point, though no date has been firmly attached to this example. The interior of the fort slopes gently down toward the northeast and is now featureless, stripped of whatever structures or activity once defined it. The cluster of three forts in the area was documented as part of Markus Casey's 1999 survey of coastal promontory forts across counties Sligo, Mayo, Galway, and Clare.