The site is a rath, the Irish term for a roughly circular earthwork enclosure, typically dating from the early medieval period and used as a farmstead, that sits in level grassland and has been worn down considerably over the centuries. Where it once would have presented a continuous raised boundary, it now offers only partial clues: a stone-faced bank surviving at the south-east, and elsewhere a scarp, the kind of low slope or cut in the ground that marks where an earthwork once stood more confidently. A ring of trees and bushes traces the perimeter, which is often the clearest indicator of a rath's outline when the earthwork itself has faded.

The enclosure is roughly subcircular in plan, measuring thirty-seven metres north to south and thirty-three metres east to west. A gap at the south-east may be an original entrance, the point through which the inhabitants of the enclosed farmstead would once have passed. More striking, though, is what has happened at the north-north-east: that section of the monument has been quarried out, removing whatever earthwork or stonework once stood there. Quarrying of this kind was common across Ireland, where the stone-faced banks of raths were a convenient source of building material, and the slow dismantling of ancient enclosures was rarely understood as loss at the time. What remains at Loonaghtan is enough to read the shape of the place, but only just.