The reason is a slight depression in the soil, roughly twenty metres long and eight metres wide, within which the ploughsoil sits a little lower than it should. At the centre of that hollow lies a single large capstone, about a metre in length and just over half a metre wide, embedded below the surface and oriented along an east-south-east to west-north-west axis. Its upper surface is triangular in section, and pieces have been chipped away over time, almost certainly by passing plough blades. That capstone is the only thing currently visible of what lies beneath: a souterrain, an underground stone-built passage or chamber system of early medieval Irish construction, typically used for storage, refuge, or both.

A video of the interior, provided to the National Museum of Ireland, reveals rather more than the surface suggests. The souterrain is T-shaped in layout, consisting of a low passageway leading from a small corbelled beehive chamber, the kind of space built by laying stones so that each course slightly overhangs the one below until the walls meet or can be capped with flat lintels. The walls themselves are composed of crude angular and rounded boulders. At a right angle to this first passageway runs a taller one, intersecting it to form the T. One end of the system is blocked by roughly coursed boulders, while the other may terminate in a drop-hole, a feature sometimes found in souterrains where a sudden change in floor level would have hindered anyone unfamiliar with the space from moving quickly through it in the dark. There are areas of partial collapse throughout, leaving an uneven floor. The entrance, once located approximately thirteen metres downslope from the capstone, has been infilled at some point in the past; no variation in soil colour or texture remained to indicate exactly when.

The site sits in an arable field along New Road, with housing now occupying the north-east corner of the same field. There is no current access to the souterrain itself, and the entrance is sealed. What a visitor can observe above ground is modest: the oval area of slightly lower ground, the exposed capstone at its centre, and one adjacent boulder to its side. The field is in active agricultural use, so movement within it is constrained by the growing season and the practicalities of working farmland. The capstone is most legible when the field has been recently planted and the ridge-and-furrow pattern of cultivation throws the hollow into subtle relief.