It occupies a slightly raised circular platform, roughly 33 metres north to south and 34 metres east to west, and what is left of its enclosing earthworks has been worn down unevenly over the centuries, so that one arc reads clearly while another has nearly dissolved back into the field. A loose ring of hawthorn trees follows the circuit, a detail that feels incidental but is not; hawthorn has long been associated with ringfort boundaries in Ireland, and its presence here quietly marks out the perimeter where the earthworks themselves grow faint.

A rath is an early medieval enclosure, typically of the first millennium AD, built of raised banks and ditches to define and protect a farmstead or the dwelling of a person of some local standing. At Mannin, the inner bank is best preserved on the western arc, where it reaches 3.6 metres in width, while the eastern arc has been partly levelled. Outside the main bank runs a fosse, a defensive ditch roughly 2 metres wide, accompanied by a low external bank of similar width. Both are clearest on the south-east and west arcs; to the north and north-east they have been lost entirely. The interior was apparently built up at the south and south-west to level the ground, and a gap of about 2.5 metres in the bank at the south-east, with what may be a causeway crossing the fosse, suggests the original entrance. A possible souterrain, an underground passage or chamber often used for storage or refuge, has been identified in the south-west quadrant, adding a further layer of complexity to what the site may once have contained beneath the surface.