Beneath the unremarkable field lay a souterrain, an underground structure of the kind built throughout early medieval Ireland, typically as a place of refuge or cool storage, consisting of chambers connected by low, narrow passages called creepways through which a person would have to crawl. The accidental collapse was the only indication that anything was there at all.

Following the discovery, the site was investigated by M. J. O'Kelly and E. M. Fahy of University College Cork. What they found was a system of four oval-shaped, earth-cut chambers with barrel-vaulted ceilings, arranged in a rough sequence and connected by creepways at their corners and ends. The chambers vary in size; the largest, chamber 1, measures roughly three metres long, 1.7 metres wide, and 1.8 metres high, while the others are somewhat lower and narrower. Chamber 1 retains a blocked creepway in its north wall and a blocked shaft that once led to the surface at its east end. Chambers 2 and 3 both have short recessed stone walls, and a long passage extending from chamber 4 could not be fully explored because of further collapse. The investigators concluded that the whole complex was likely dug from a single construction pit, with the stone walls and blocked passages representing later modifications or deliberate closures within the original structure. The reference to McCarthy (1977) places the site within a broader regional study of Cork souterrains, though no artefacts or dating material from the Knockane example appear to have been published.