Local accounts describe a souterrain, an underground tunnel of the kind built in early medieval Ireland, typically for storage or refuge, constructed from drystone walls with flat lintel stones laid across the top to form a roof. This one reportedly ran for somewhere between fourteen and eighteen metres before ending in a section of collapse, where the roof or walls have given way. That abrupt termination is probably the reason it survives at all in local memory; someone went in far enough to know where it stopped.

The souterrain sat within a rath, a type of enclosed farmstead once ringed by an earthen bank and ditch, common across Ireland during the early medieval period. Souterrains were frequently built within raths, and the two features together suggest a settlement of some significance in the landscape at Johnsfort. What makes this particular case quietly melancholy is the fate of the enclosure itself. The rath was levelled during the 1980s, a decade when many such earthworks were lost to agricultural improvement and land clearance. The bank and ditch that once defined the site are gone. The souterrain, being underground, was harder to remove, and so it persists, sealed and largely inaccessible, beneath ground that no longer shows any surface trace of the structure it once belonged to.