It was roofed with stone lintels and, at some point, an opening into it was uncovered. That is more or less the full extent of what is recorded. Today, there is no visible trace.

The tunnel belongs to a category of underground passage known as a souterrain, a type of stone-lined or rock-cut structure commonly found in early medieval Ireland, typically associated with ringforts or raths. Raths were enclosed farmsteads, usually circular, defined by one or more earthen banks and ditches, and they were the dominant settlement form across Ireland from roughly the fifth to the twelfth century. Souterrains built within them served various purposes, most likely secure storage for food or valuables, and possibly as places of refuge. The one at Corkagh More lies within or beside a rath, and what little is known of it comes from local information rather than any formal excavation. The stone lintels described are characteristic of the type: flat slabs laid horizontally across upright side walls to form a corbelled or capped roof passage, often narrow enough to require stooping or crawling.