What came to light then was a souterrain, an underground stone-lined or earth-cut passage or chamber used in early Irish society variously for storage, refuge, or both. The Moneygaff example is modest but well-defined: two chambers sitting side by side beneath the soil, their ceilings low enough that no adult could stand upright inside.

When Cleary documented the site in 1981, the two chambers were found to be earth-cut rather than built from stone, which places them among the simpler end of the souterrain spectrum. The first chamber is roughly square, measuring three metres in length by 2.8 metres wide, with a ceiling height of just under a metre. The second is slightly narrower and oval in plan, sharing the same length and ceiling height as the first. What makes the second chamber particularly interesting is a construction shaft in its north wall, which would have been used as an access point during the original digging, and a possible air vent in the east wall, suggesting that whoever built it gave some thought to keeping the interior liveable, at least for short periods or for whatever was being stored there.