The souterrain, an artificially constructed underground passage or chamber typically built during the early medieval period and associated with nearby settlement, has been backfilled. Whatever was once accessible beneath the surface has been deliberately closed off, leaving the grass unbroken and the field indistinguishable from any other.

The site sits approximately forty metres to the south-east of a ringfort, the kind of circular enclosed settlement that was common across Ireland between roughly the sixth and twelfth centuries. Souterrains were frequently built in close association with ringforts, likely serving as places of refuge, cool storage, or concealment. At Knockeenboy, the connection between the two features suggests the underground structure was once part of the same broader settlement complex. What is known about the souterrain comes from local information rather than excavation, and at some point after it was identified, the chamber was backfilled. No visible surface trace now remains.