The site belongs to a category of early medieval underground structures known as souterrains, typically dry-stone tunnels or chambers built beneath raths, the circular earthwork enclosures that served as farmsteads across early medieval Ireland. Their precise purpose is still debated, though storage and refuge are the most commonly cited functions. What makes Brackloon quietly peculiar is not what survives but what has been deliberately sealed away and forgotten.

The souterrain is said to lie in the south-western quadrant of a rath at Brackloon, and local tradition holds that an access hole, positioned close to the bank on the south-south-western side, was at some point blocked up. No record explains when this happened or by whose decision. What remains is a piece of landscape knowledge passed down through the community rather than confirmed by excavation or survey, a kind of folk memory of an opening that once existed and was then quietly closed off. The rath itself survives as a mapped feature, but the souterrain beneath it has left nothing visible at ground level for anyone standing above it today.