At this rath in Ballybeg, County Mayo, the administrative line dividing the townlands of Tullaghaun and Ballybeg cuts clean through the interior on a roughly north-north-east to south-south-west axis, with a perpendicular field wall branching off eastward across the south-east quadrant. The monument has effectively been parcelled up by later land management, with short sections of its enclosing bank absorbed into field walls at the north-north-east and south. None of this has erased the structure; it sits visibly on a ridge in pasture, with wide views in most directions, interrupted only by a natural undulation in the ridge to the north and north-east. About 150 metres to the south-west, a north-south esker, a long gravel ridge deposited by glacial meltwater, runs through the landscape below.

The rath itself is a roughly circular enclosure, measuring approximately 37 metres east to west and 36.5 metres north to south, defined by an earth and stone bank from which large stones protrude along the outer slope. A rath is an early medieval enclosed farmstead, typically dating from somewhere between the sixth and tenth centuries, and this example retains enough of its form to read clearly on the ground. Within the level interior, a subcircular raised area roughly 13 to 14 metres in diameter occupies the centre and northern half, defined on its western and northern sides by a scarp almost a metre high. At the north-west of this raised area there is a curving depression, between 1.5 and 3 metres wide and 0.7 metres deep, that arcs from south-west to north-east before terminating against the townland wall. This may be the collapsed or filled remains of a souterrain, an underground stone-lined passage or chamber associated with early medieval settlement, often used for storage or refuge. A second shallow depression, roughly 5 metres by 2.6 metres, sits against the inner edge of the bank in the north-east quadrant, its purpose unrecorded.