The enclosure it once served has vanished entirely from the landscape, yet the entrance remains: a neat lintelled opening, just 1.3 metres wide and 0.3 metres across, set into the northern slope of the rise as though waiting to be noticed.

This is a souterrain, an underground stone-built passage or chamber constructed during the early medieval period in Ireland, typically associated with ringforts or other enclosed settlements. They were used variously for storage, refuge, or as escape routes, and the craftsmanship of their construction often outlasts every other trace of the site they belonged to. The Ballard example follows the entrance with a passage 2.3 metres long that slopes sharply downward, reaching a depth of 1.2 metres below ground level. The walls are drystone construction, meaning no mortar was used, and they corbel slightly inward as they rise, a technique where each successive course of stone is set a little further inward than the one below, lending subtle structural stability. The stonework is notably careful, built from regular courses of flat slabs with larger slabs reserved for the lower courses where the pressure is greatest, and the whole passage is roofed with slabs. At the far end, a small secondary opening, only 0.3 metres high and requiring anyone passing through it to crawl, appears to lead into a further passage beyond. Whether that second passage was a functional extension or a deliberate dead end used to slow an intruder is not recorded. The surrounding enclosure that would have explained the souterrain's original context has left nothing visible above ground.