The rath, a circular raised enclosure of the kind used as a farmstead during the early medieval period, has long since been levelled, but the souterrain it once contained remains largely intact beneath the surface.

A souterrain is an underground passage or chamber, usually earth-cut or stone-lined, associated with early medieval settlement in Ireland. They served various purposes, most likely as cool storage spaces, places of refuge, or both. The Ardea example is entered through an opening roughly one and a half metres long and less than a metre wide, which leads north-westward into the main chamber. That chamber measures approximately three and a half metres along its north-west to south-east axis and sits about half a metre below ground level, with a curved roof just over a metre high. From the south-west wall, a creep-hole, barely sixty centimetres wide and forty centimetres high, extends a further two metres; the term refers to a deliberately constricted passage that would have forced anyone entering to move slowly and with difficulty, a feature that may have been defensive in purpose. Two blind offshoots, passages that lead nowhere, were also recorded at the eastern and south-eastern sides of the chamber. Whether these were unfinished extensions, collapsed tunnels, or intentional dead ends is not known.