A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts, and built for purposes that archaeologists still debate, including storage, refuge, or ventilation for a nearby dwelling. At Garland, the feature survives only as local tradition and as an entry in the archaeological record. The passage, if it ever existed in the form people remembered, has since been infilled.

The ringfort with which this souterrain is associated sits within a landscape of West Cork that retains a remarkable density of early medieval settlement remains. Ringforts, roughly circular enclosures defined by earthen banks or stone walls, were the dominant farmstead type in Ireland from around the fifth to the twelfth century, and souterrains were commonly incorporated into them. The tradition of an underground feature at Garland was recorded and published in the Archaeological Inventory of County Cork, Volume 1, which appeared in 1992. By the time that record was compiled, the souterrain had already been infilled, leaving nothing visible at the surface. What survives is essentially a memory of a feature rather than the feature itself.