Between those two cuts in the rock, there is a slot that may once have supported a drawbridge. The inner fosse is flat-bottomed, four metres wide, and bounded on its seaward side by a near-vertical rock face dropping roughly 3.5 metres, with a low ramp surviving at its southern end. These are not modest earthworks; they represent a deliberate and labour-intensive reshaping of the headland's geology. And yet, above ground, there is nothing else. No wall, no tower, no trace of whatever structure the defences were built to protect.

The historical context sharpens the mystery considerably. In 1651, a warrant was issued to Colonel Richard Townshend authorising the construction of a new fortification to defend Castlehaven. The timing is significant: this was the final, grinding phase of the Cromwellian conquest of Ireland, and Castlehaven, a natural harbour of some strategic value on the south-west coast, would have been a legitimate concern for the new military administration. The fosses cut into the promontory's neck almost certainly represent the physical result of that 1651 warrant, though whatever was built above them has left no mark on the surface. Whether the fortification was completed, demolished, or simply never built in permanent materials is unknown.

The site is accessible as a landscape feature rather than a monument in any conventional sense. A visitor who knows what to look for, specifically the two rock-cut channels across the promontory's neck and the surviving ridge between them, will find the engineering legible enough on the ground. The vertical rock face on the seaward side of the inner fosse is the most striking element, and the low ramp at its southern end gives a sense of how the space was intended to be used. What is absent, the vanished structure above, is in some ways as interesting as what remains.