What is known amounts to a single observation: around 1883, a chamber was uncovered at the entrance to Firville House. That is more or less where the story ends.

The chamber in question would almost certainly have been a souterrain, an underground passage or cell built during the early medieval period, typically from dry-stone walling and roofed with large slabs. Souterrains are found across Ireland and were associated with nearby settlements, most likely used for cool storage or as a place of refuge in times of danger. The one at Bealick was noted by McCarthy in 1977, drawing on what appears to have been a local account of the 1883 discovery. No excavation record survives, and no surface feature marks the spot today.