Nobody was looking for it. It came to light only when ground-levelling machinery moved in ahead of construction work, cutting into the south-facing slope and exposing something that had lain undisturbed for centuries. A souterrain, to use the proper term, is an artificially constructed underground structure, typically associated with early medieval settlement in Ireland, and thought to have served for storage, refuge, or both. This one is more elaborate than many.

The main passage follows a WSW-ENE axis, curving gently as it goes, with a floor that slopes gradually downward in keeping with the natural lie of the land. Its dimensions are tight, roughly a metre high and less than a metre wide in places, the kind of space a person would have to crouch and squeeze through. Off the western side of this passage, a short connecting section, just one and a half metres long, opens into a circular chamber about five metres in diameter, its walls showing traces of corbelling, the technique of laying stones so that each course projects slightly inward to form a rough vault or dome. The chamber itself was unroofed by the time of discovery. A sherd of medieval pottery found in the upper fill of the chamber suggests it had already collapsed during the medieval period. A second passage section leading toward the chamber was uncovered during further groundworks. Archaeological investigation in the wider area, reported by Clinton in 1998 and Kavanagh in 2011, also revealed a bivallate ringfort nearby, meaning a ringfort enclosed by two concentric earthen banks, as well as traces of an early medieval field system, placing the souterrain within what was clearly a more extensive early settlement landscape.

The site has since been covered over again and is not accessible to visitors. What remains is the record: measured, documented, and folded into the broader picture of early medieval Dublin that continues to emerge, piece by piece, from beneath fields and building sites across the county. The finds and site records are held within the national archaeological archive, and anyone with a serious interest in the subject will find Clinton's 1998 publication the most detailed treatment of the structure itself.