Roughly 38 metres across, the earthwork retains intermittent traces of both inner and outer stone revetments along its northern and eastern arc, the dressed or laid stone faces that would once have reinforced the bank and given the whole structure a more solid, finished appearance. The narrow gaps at the ENE and ESE are considered modern intrusions, small breaks in the perimeter that probably came long after the fort fell out of use.

What gives this particular site its quiet interest lies just inside the bank at the southwest. There, a grassy rectangular hollow runs northeast to southwest, roughly 11 metres long, 3 metres wide, and averaging about 2 metres in depth. A flanking mound of earth runs alongside it, and stones are visible at its base. Archaeologists have identified this as a possible souterrain, an underground or semi-subterranean passage or chamber typically built during the early medieval period in Ireland. Souterrains were generally constructed of drystone walling roofed with large lintels, and their exact function is still debated; they may have served for cold storage, as refuges, or both. The Mylespark example has not been excavated, and its full extent remains uncertain, which is part of what makes it interesting. The hollow and its accompanying earthwork are suggestive rather than conclusive, a feature that invites attention without yet giving up its answers.