It looks and behaves like a souterrain, the type of stone-lined underground tunnel built throughout early medieval Ireland, often for storage or refuge, but it is not quite one. Rather than being cut beneath the ground, it is constructed within a raised terrace of earth and stone, making it a lintelled creepway, a narrow passage roofed with large flat slabs, built into the fabric of the landscape rather than dug through it.

The feature sits in the western half of the monastic enclosure known as The Cashel, running from the area in front of Teach Molaise, the small oratory associated with the island's founding saint, towards the south-west corner of Templenatinny, one of several early churches within the enclosure. The Cashel itself is a remarkable survival, a walled monastic complex on a small Atlantic island that was abandoned by its permanent population in 1948 but retains an unusual concentration of early medieval structures. The creepway was documented during an archaeological survey carried out between 1998 and 1999, the results of which were published in 2008 by J. O'Sullivan and T. Ó Carragáin. Surveyors were unable to examine the interior in detail because the roof lintels, the same large flat stone slabs that give the passage its form, were judged to be at risk of collapse.

That instability is itself worth noting for anyone who reaches this spot. The passage cannot be entered safely, and should not be. What can be observed is the broader context of the raised terrace in which it sits, a subtle but deliberate shaping of the ground that makes the western subdivision of The Cashel feel architecturally considered in a way that goes beyond simple enclosure walls.