Roughly thirty metres in diameter, it sits on a west-to-east sloping field that was once classified as poor marginal land, and when investigators visited the site in 1986, the monument was entirely invisible at ground level. It only becomes legible from the air, where it resolves clearly into a circular form, as aerial photography has confirmed on more than one occasion.

Circular enclosures of this kind are a common feature of the Irish landscape and may represent the remains of a ringfort, a defined farmstead type used from the early medieval period onwards, or an even earlier enclosure of uncertain purpose. What makes the Spahill example quietly odd is the combination of its imperceptibility on the ground and the way the surrounding environment has since adapted around it. The site now sits entirely within forestry, but a circular area of approximately forty metres has been deliberately left free of planting, creating a kind of sylvan negative space that corresponds to where the enclosure lies beneath the surface. There is also a meandering former river course around sixty metres to the north, a detail that would have made this marginal ground somewhat more significant in an earlier era, when water access shaped where people chose to settle or enclose land.

For anyone who does visit, the clearing within the forestry is the most tangible thing to look for. The enclosure itself will not announce its presence underfoot, but the unplanted circle, wider than the monument it protects, gives the location a peculiar quality, a deliberate absence where the trees simply stop.