What remains is just enough to read: a gallery, roughly 4.6 metres long, tapering in both height and width as it runs towards the north-north-east, which is characteristic of the wedge tomb type. Wedge tombs, the most numerous of Ireland's megalithic monument classes, are so named for this narrowing profile, and most date to the late Neolithic and early Bronze Age, broadly between 2500 and 2000 BC.

The stonework at Foilnamuck preserves several distinct elements despite the losses. A septal stone, a slab used to divide or close off a section of the internal chamber, marks the south-south-west end of the gallery, though it now sits partly embedded in a field fence, absorbed into the working landscape of a later era. On the southern side of the gallery, four sidestones survive; two positioned closely together at the south-south-west end, and two smaller examples standing separately further along towards the north-north-east. A thin slab set outside the junction of the paired southern stones carries one end of a roofstone, its other end resting on a pad-stone placed above the western upright on the northern side. That northern upright is accompanied by a further stone outside it, which appears to be a lone remnant of what was once a close-set outer walling, a feature common to wedge tombs, which often had a double-walled outer skin encasing the main gallery. One small set stone beyond the easternmost of the three contiguous northern stones resists easy classification; its function, as Ruaidhrí de Valera and Seán Ó Nualláin noted in their 1982 survey of megalithic tombs across Munster, remains uncertain. That combination of careful documentation and honest uncertainty captures something of what makes this kind of monument compelling: even in its diminished state, not everything here has given up its meaning.