From a distance it reads as a slight rise in the field, but up close the archaeology resolves into something more deliberate: two concentric banks with a fosse, the ditch between them, enclosing a roughly circular area some 33 metres in diameter. It is in fair condition, which is perhaps more than might be expected given that cattle have worn gaps through the inner bank at multiple points, though a two-metre opening on the eastern side may be original, a genuine entrance used by people rather than livestock.

The site belongs to the broad category of raths, the ringforts that are among the most common early medieval monuments in Ireland, typically dating from roughly the fifth to the twelfth century and used as enclosed farmsteads or seats of local status. What makes Plumbtree Fort a little more layered is the possibility that it did not function solely as a rath. Writing in 1912, a researcher named Holt recorded a possible bailey to the east of the enclosure. A bailey is the outer courtyard associated with a Norman motte-and-bailey castle, and its presence here, if confirmed, would suggest that the site may have been reused or adapted after the Anglo-Norman arrival in Connacht during the late twelfth century, a practice not unknown elsewhere in Ireland where earlier earthworks were pressed into new service. Within the western sector of the interior there is also a possible hut site, hinting at domestic occupation within the enclosure itself. Field walls from later periods have been laid directly over the outer bank and cut across it at the south, the ordinary agricultural past of the landscape gradually overwriting the earlier one without quite erasing it.