This is the creepway, a deliberately restrictive connecting passage typical of souterrains, the drystone-built underground structures of early medieval Ireland that were used for storage, refuge, or both. The deliberate awkwardness was the point: any pursuer would be forced to enter headfirst and defenceless.

The Glanlough souterrain is L-shaped, consisting of two rectangular chambers joined by a low crawlspace just 39 centimetres wide and 58 centimetres high. The first chamber runs roughly north to south and was built with pronounced corbelling in its upper courses, meaning the stones were laid with a gradual inward lean, narrowing the chamber from 1.2 metres at its base to as little as half a metre near the roof. The northern end of this chamber has partially collapsed, its roofing slabs having fallen inwards and filled the space with debris to within 40 centimetres of the ceiling. Because no separate entrance has been identified anywhere else in the structure, archaeologists believe the original entry point was somewhere in this now-ruined northern section, either through the roof or the eastern wall. The second chamber, better preserved, runs east to west and measures 4 metres long; its walls incline inward to support nine roofing slabs, reducing the internal width at roof level to around 65 centimetres. The whole structure sits roughly 15 metres from the western bank of a small river, in open moorland shaped long before any human occupation by the movement of glaciers through the valley. The site was recorded by J. Cuppage in the 1986 Dingle Peninsula archaeological survey of the Corca Dhuibhne region, a landmark survey of one of the most archaeologically dense peninsulas in Ireland.