What makes this fort unusual is not any grand scale but a particular detail at its centre: a small circular hut-site, roughly seven to eight metres across, defined by its own low earthen bank, sitting inside the larger enclosure with no identifiable entrance. Whatever structure once occupied that inner ring, the means of getting in and out of it has either vanished or was never built in a way that left a trace.

The site belongs to the broad category of earthwork enclosures, sometimes called raths or ringforts, that are found throughout Ireland and generally date to the early medieval period, roughly between the fifth and twelfth centuries. They functioned as enclosed farmsteads, the banks and ditches providing security for livestock and a household rather than any kind of military fortification in the modern sense. At Drumguillew, the arrangement follows a recognisable pattern: an inner earthen bank separated from a further outer bank by a fosse, which is a defensive ditch. Much of both banks has been broken by gaps over the years, and the outer bank has been partly swallowed into the field boundary system to the north-east and south. What survives intact is the original eastern entrance, a causeway across the fosse roughly four metres wide and about forty centimetres high, leading through the inner bank at its base width of just over two metres. The overall enclosure measures approximately 46 metres north to south and 37 metres east to west, a subcircular footprint that follows the natural contour of the drumlin summit.