The structure is modest in its surviving dimensions, roughly 18.6 metres east to west and 15 metres north to south, yet its persistence is the interesting part. Built in the drystone manner, meaning without mortar, relying instead on the careful fitting of stones against one another, the wall has narrowed as it rises and now stands only around 0.7 metres high. That it protrudes at all above the surrounding bog suggests the bog has grown up around it over time, gradually swallowing whatever ground level once applied when the enclosure was in use.

The wall retains two distinct breaks, one at the south-west measuring three metres across and one at the south-east measuring five metres, which are most plausibly the original entrances, both oriented towards the downslope and the valley below. The function of such enclosures is not always straightforward to determine. They could have served as livestock pounds, small farmsteads, or structures with a more ceremonial or territorial purpose, and without excavation the Annagh Beg example keeps its purpose to itself. What complicates any reading further is that modern field boundaries now abut the enclosure on its eastern and western sides, meaning the landscape around it has continued to be organised and reorganised long after whatever use the enclosure originally served had ended.