It is a small but genuinely odd detail in an otherwise rough-built drystone enclosure, and it sits within a cluster of monuments, including a holy well, a stone altar, a cell, and a nearby mound, that together suggest a place of some accumulated significance. The cashel, a term for a roughly circular stone-walled enclosure of the kind found across early medieval Ireland, occupies a level but frequently waterlogged patch of pasture in Capnagower, looking out toward the shoreline and Kinnacorra Point some 250 metres away.

The 1840 Ordnance Survey map shows the enclosure as a small trapezoidal shape, roughly 15 by 12 metres, which means that by the time the antiquary T. J. Westropp visited for the first Clare Island Survey in 1911, the structure had already been substantially altered. Westropp noted that it was "evidently rebuilt, even in recent times", observing that the western and southern walls had been heavily reworked while the foundations and set slabs remained in place and the northern and eastern portions retained more of their original fabric. He described the plan as "irregularly quadrilateral, with rounded corners"; it is now understood as roughly circular, measuring about 17 metres across in each direction. The double-faced drystone wall, built largely of large limestone blocks with some sandstone visible especially near the entrance, survives well along the southern and western arc but has collapsed considerably elsewhere. In one eastern stretch, the only indicators of the wall's former line are two massive upright slabs still standing to 0.65 metres. Where Westropp once found a bushy hollow, the enclosure is now clear of any shrubby vegetation. Local tradition associates the whole cluster of monuments here with Granuaile, the sixteenth-century seafaring figure Grace O'Malley, whose connections to Clare Island are deep and long-remembered.