The roughly oval enclosure measures around 46 metres at its longest and 39 metres across, and what survives is not simply a single bank and ditch but a double line of earthworks: an inner bank, a fosse (a dug defensive ditch), and an outer bank beyond that, with an outer drain running along the northern arc. The entrance, still discernible, lies to the south-east, where a causeway crosses the fosse and gaps in both the inner and outer banks align to form a passage into the interior. The earthen bank is overgrown now, but at the south-east it still stands to an external height of around 1.4 metres, and at the east-north-east the scarp face rises to nearly 3 metres.

This is a ringfort, or rath, of the kind built throughout early medieval Ireland, typically between the sixth and tenth centuries, as a defended farmstead or the residence of a local lord. What sets Lisboy apart from a straightforward example of the type is the added presence of a souterrain, an underground stone-lined passage or chamber used for storage and possibly refuge, whose entrance opens at the lip of the outer fosse on the east side. The combination of double earthworks and a souterrain points to a site of some local significance. There is also a second rath immediately to the south-west, making this a paired enclosure of the sort occasionally found where a higher-status settlement warranted additional or satellite enclosures nearby. Archaeological testing carried out by R. Meenan around 80 metres to the north-east, as part of work recorded in 2005, produced no material related to the fort, leaving the immediate question of its occupation history open.