The logic was pragmatic: any ancient stone structure large enough to shelter a person became, in oral tradition, one of the couple's many beds as they fled across the country from the pursuing Fionn Mac Cumhaill. The example at Derrycallan in County Galway is a wedge tomb, a type of megalithic monument built during the late Neolithic and early Bronze Age, typically consisting of a narrow stone-lined gallery that widens and rises at one end. This one is modest in scale, just two metres long, its chamber tapering from roughly 1.8 metres wide at the south-west end to 1.4 metres at the north-east, and decreasing in height from west to east. A single slab closes the south-western end, and a roofstone covers the chamber above.

The tomb sits in gently rolling pastureland, with Ballynakill Lough lying about 400 metres to the north. Sections of outer-walling survive along the southern side and more substantially around the north-eastern end, and the whole structure is set within a small earthen mound that rises close to roof height, partially embedding the stonework in the landscape. The monument is documented in Ruaidhrí de Valera and Seán Ó Nualláin's Survey of the Megalithic Tombs of Ireland, Volume III, published in 1972, which catalogued wedge tombs and other megalithic forms across the midlands and western counties. The Derrycallan tomb is a quiet, well-preserved example of a type found with some frequency in Connacht, its folkloric name connecting a structure that is several thousand years old to a medieval romance cycle that had nothing to do with its original builders.