The cashel at Lettergesh sits directly above the pass between Lough Fee and Lough Muc, a position that would have given whoever built it a clear view of movement through a natural corridor in an otherwise rugged landscape. A cashel is a stone-walled ringfort, typically circular or oval, constructed from dry-laid stone without mortar, and this one follows that tradition closely, its perimeter wall now much collapsed but still legible as a boundary.

The enclosure is oval in plan, measuring roughly 24.5 metres on its longer axis and just under 16 metres across, with a possible entrance facing south-east. Against the inner face of the wall on the south-south-west side, there are traces of what may have been a semicircular hut, the kind of structure that would have sheltered people or animals within the protected interior. The site was noted by Lynam in 1922, who recorded it in a survey of the area, and it remains in fair condition despite the wall's partial collapse over the intervening centuries. Ringforts of this type were built across Ireland broadly during the early medieval period, and though many sat in lowland farming country, hilltop examples like this one suggest that control of passage or visibility over a route was sometimes as important as agricultural convenience.