In 2003, contractors preparing to widen a road that cuts east to west through the centre of an earthwork known as Lisheenmoyle, a rath or ringfort of the kind once used as a defended farmstead in early medieval Ireland, sliced through the edge of something much older and more deliberate. What emerged in section from the exposed embankment was a carefully constructed drystone wall, built from large and medium-sized limestone rubble with smaller stones packed into the gaps, suggesting the outer face of a souterrain chamber. A souterrain is an underground stone-lined passage or chamber, typically associated with Irish raths and used variously for storage, refuge, or ventilation of an adjoining structure. The wall here measured 1.6 metres wide and 1 metre high, its upper western edge pressing against a large natural limestone boulder, and its base sitting exactly at subsoil level, as though the builders had worked down to the bedrock and used what they found there.

The rath itself appears on Ordnance Survey six-inch maps from both 1838 and 1929 under the name Lisheenmoyle, suggesting it was a recognised feature of the local landscape long before anyone investigated what lay beneath it. The 2003 excavation, carried out under licence reference 03E0955 by King, was limited strictly to the road cut and concentrated on the southern portion of the rath. Because the possible souterrain was exposed only in section, its full extent remains unknown. The wall was recorded in detail and then left in place, sealed once again inside the embankment rather than excavated further or removed. What was found amounts to a partial glimpse, a single face of what may be a chamber that still extends unexcavated into the body of the rath, waiting beneath the soil on either side of a Mayo roadway.