It is the kind of place that exists in the archaeological record but not in any conventional sense of public awareness, sitting quietly on a level terrace on the upper north-east facing slopes, with the surrounding land giving only faint hints that something deliberate was built here.

A souterrain is an artificially constructed underground passage or chamber, typically of early medieval Irish date, built from drystone walling and roofed with flat lintels. They are found across Ireland and are generally associated with settlement enclosures, used variously for storage, refuge, or both. The example at Coars follows a recognisable pattern but has its own particular arrangement. The entrance, just 0.75 metres wide and 0.45 metres high, opens into a first passage running westward for roughly three metres, its walls roughly coursed and its floor laid with an even spread of stones. Three upright slabs are set against the southern side-wall, their precise function unclear. At the western end, the passage narrows dramatically into a creepway, a deliberately tight connecting gap formed by two jambs and a lintel, measuring only about 0.56 metres high and 0.38 metres wide. This squeezing point would have slowed any unwelcome entry considerably. Beyond it lies a second chamber, aligned roughly north to south, at least five metres long, with a small air-vent near the top of the northern end-wall. Its southern end is currently blocked by an accumulation of earth and stone, so the full extent of the structure remains unknown. A semicircular ring of boulders lies a short distance to the south, and an ill-defined bank runs for about eight metres to the east; these features may point to an associated above-ground structure, though their condition makes any firm interpretation impossible. The survey of the Iveragh Peninsula compiled by A. O'Sullivan and J. Sheehan, published by Cork University Press in 1996, recorded both aspects of this site and remains the principal source of what is known about it.