It does not announce itself dramatically. The ground simply rises into a grass-covered platform, roughly thirty metres across, shaped by human hands at some point during the early medieval period, when such enclosures were a common feature of the Irish countryside. There are tens of thousands of ringforts scattered across Ireland, yet each one carries its own particular relationship with the land around it, and this one was clearly positioned with some deliberation, set on a terrace that commands a view down to the water below.

A ringfort, or rath, was typically the enclosed homestead of a farming family, the earthen bank serving as a boundary and a modest defence against livestock straying or neighbours encroaching. At Islandgar, the enclosing bank measures between 4.2 and 5 metres wide, and survives to an external height of around 1.2 to 1.4 metres across much of its circuit, dropping to roughly 0.8 metres on the eastern side. The interior of the bank stands considerably lower, between 0.2 and 0.4 metres, suggesting the raised platform of the interior has partially levelled over time. Where the natural slope of the hillside does some of the defensive work, to the west, the bank gives way to a scarp, a cut or drop in the ground, standing about 1.4 metres high. There are also faint traces of a fosse, a defensive ditch, surviving to a depth of around 0.2 metres along the southern arc of the site. The whole structure is grassed over now, the bank blending into the surrounding slope with the unhurried ease of something that has been there for more than a thousand years.