What survives at Knocknageeha is the skeletal remains of a court tomb, one of the oldest monument types in Ireland, built by Neolithic farming communities perhaps five thousand years ago. Court tombs typically feature an open forecourt leading into a roofed gallery, the whole structure originally buried beneath a long cairn of stone and earth. Here, the cairn itself may still be present, lurking beneath the vegetation that has quietly consumed the site.

The gallery, running roughly northeast to southwest and measuring around five metres in length, retains enough of its original structure to read as a deliberate architectural sequence. A single jamb stone, standing 1.2 metres high, marks the eastern entrance, with a displaced stone leaning nearby that may once have formed the opposite jamb, framing a threshold that people crossed for ritual or funerary purposes across many generations. Three stones define the northern wall of the gallery; a single sidestone survives on the southern side. At the southwestern end, one closing stone remains, though it now leans outward, as though tired of the effort. Most telling is a segmenting jamb, roughly a metre high, that divides the interior into two distinct chambers: a front chamber of about two metres and a deeper rear chamber of nearly three. This two-part arrangement is characteristic of court tombs across the west of Ireland and suggests the space was used in structured ways, perhaps separating different stages of burial rites or different categories of the dead. The site was recorded and described by Ruaidhrí de Valera and Seán Ó Nualláin in their 1964 survey of Mayo's megalithic tombs, a landmark work that systematically documented monuments that had otherwise passed largely unnoticed by formal scholarship.

The site lies on undulating pasture on the northern side of a ridge that drops away sharply to the northeast. The overgrowth that surrounds the stones makes close examination difficult, but it also preserves what remains from further disturbance. Anyone approaching should expect to work for the view, moving carefully around vegetation to distinguish the standing and fallen stones from the surrounding landscape.