That is barely wide enough to squeeze through and not tall enough to enter upright. Local tradition holds that it leads to an underground passage. The opening is now closed up with stones.

A souterrain is a man-made underground structure, typically a stone-lined tunnel or chamber, built during the early medieval period in Ireland and used variously for storage, refuge, or concealment. The Glenlough example sits within a pair of conjoined huts, specifically the more westerly of the two, and its entrance cuts through the inner face of the enclosing bank. That placement, folded into the fabric of the hut itself rather than standing apart, is a reasonably common arrangement, though the fact that its full extent remains unrecorded gives it an unresolved quality. What lies beyond the sealed opening is known only by local account, and those accounts do not go into detail.