Measuring just 0.6 metres wide and 0.25 metres high, this lintelled entrance, framed by a flat capstone laid across its top in the manner typical of such structures, gives onto a stone-built souterrain that nobody has been able to enter in recorded times.

A souterrain is an underground passage or chamber, usually dry-stone built, that appears frequently in early medieval Irish settlement sites. They were most likely used for cool storage, refuge, or both, and on the Iveragh Peninsula they are often found in association with the remains of hut sites and enclosures. This particular example at Ardacluckeen is recorded in A. O'Sullivan and J. Sheehan's archaeological survey of South Kerry, published by Cork University Press in 1996, which catalogued the remarkable density of early settlement remains across this stretch of coastline and upland. The hut with which the souterrain is associated survives well enough for its southern angle to be clearly identifiable, yet the passage beyond the opening remains inaccessible, its full extent and form unknown.