On its summit sits a large enclosure that has been almost entirely swallowed by time. What remains is a partial arc of earthen bank mixed with loose stone, curving from the east around to the south-east, and beyond that, nothing visible at all. The enclosure would originally have measured roughly 140 metres across, which is considerable, suggesting whatever once occupied this height was meant to be seen, or at least to see.

Site enclosures of this general type, defined by a circuit of bank and sometimes ditch, appear across Ireland in various forms and periods, from later prehistoric hillforts to early medieval enclosures associated with settlement or ceremony. The precise date and function of this one at Knocknacarragh remain unresolved. What the archaeological record preserves is only geometry, a rough subcircular outline, and even that survives only in one arc. Paul Gosling's Archaeological Inventory of County Galway, published in 1993, captures the site in its current fragmentary state, relying on aerial photography alongside ground observation to confirm what little is still legible on the surface.