The enclosure is substantial, measuring roughly 76 metres east to west and 70 metres north to south, making it considerably larger than the typical ringfort, the most common type of enclosed settlement site in early medieval Ireland. Those usually measure somewhere between 20 and 50 metres in diameter, so an interior of this scale places the Seafield example in a different category altogether.

The defining feature is an earthen bank, between 2.6 and 4 metres wide, which rises internally to between 0.6 and 1.2 metres and externally to between 1.3 and 1.8 metres. Notably, there is no visible fosse, the ditch that typically runs outside a ringfort bank and whose spoil was used to build it up. Its absence here is unusual and raises questions about the site's original function or the degree to which the surrounding ground has changed over time. The bank has been absorbed into the existing field boundary along its southern to north-north-west arc, which is how many ancient earthworks survive in the Irish landscape, folded into later agricultural arrangements rather than standing apart from them. The only break in the perimeter is a modern entrance at the south. Slightly east of centre within the enclosure, a hut site has been recorded, suggesting the interior was once occupied at ground level, though the relationship between the hut and the enclosure itself is not documented. The sea lies roughly a kilometre to the north, and the terrace position would have given whoever used this place a clear outlook across the coastline.