That typographic choice is significant. Gothic lettering on OS maps was the convention reserved for antiquities, a quiet cartographic signal that whatever stands here predates the modern world by some considerable distance. The feature in question is a ringfort, known also as a rath, one of thousands of such earthworks scattered across Ireland, typically dating from the early medieval period, roughly 500 to 1000 AD, and thought to have served as enclosed farmsteads for families of some local standing.

The fort occupies the top of a prominent hill on the floor of the Glenade valley, which runs northwest to southeast through this corner of Leitrim. In plan it is subcircular, measuring roughly 34 metres east to west and 31 metres north to south across the interior, a substantial enclosed space. Its boundary is a round-topped, steep-sided earthen bank, about 2.9 metres wide, which rises roughly 0.9 metres above the exterior ground level, reaching as high as 1.3 metres at the northeastern arc. Inside, the bank stands only about 0.3 metres above the enclosed surface, suggesting significant accumulation of material over the centuries. The interior is now covered in grass and reeds. There is no visible fosse, the ditch that typically accompanies such a bank in classic ringfort construction, and no identifiable original entrance survives. A later field bank circumscribes much of the perimeter from south-southwest to north, overlaying or obscuring whatever earlier boundaries may have existed.

What lingers about Lismoyle is its quiet ambiguity. No entrance, no ditch, a name preserved in an old cartographic convention, a grassy interior that gives little away. The valley setting is specific and legible; the hill is described as prominent within it, which in a landscape like Glenade would have made this enclosure visible from a considerable distance, and would have made the world outside equally visible to whoever once lived within it.