The enclosure at Cloonlusk sits on flat ground with bogland opening out to the north and east, and what defines it is an earthen bank paired with an external fosse, the fosse being a ditch dug around the outside of the bank to reinforce the boundary. The best-preserved stretch runs from the east-south-east, around the western arc, and up to the north-north-east; elsewhere only a slight scarp, a low slope in the ground, hints at what once stood higher.

Ringforts are the most numerous monument type in Ireland, built predominantly during the early medieval period, roughly between the fifth and twelfth centuries, and used as enclosed farmsteads by families of varying social rank. Most are far smaller than this one. A diameter approaching 77 metres places Cloonlusk Fort among the larger examples, a size that in early Irish society sometimes indicated the enclosure of a person of considerable local standing. Inside the fort there is a souterrain, an underground stone-lined passage or chamber, recorded separately in the archaeological record. Souterrains are found in association with ringforts across Ireland and are thought to have served for storage, refuge, or both. Three gaps have been cut through the bank over the years, at the west-south-west, north-west, and south-east, and all three are now used as access points for farm machinery, which tells its own story about the continued life of a landscape that has been worked for well over a thousand years.