No earthwork, no visible depression, nothing. The only reason it came to wider attention in the twentieth century was that a piece of machinery broke through its roof, accidentally reopening a chamber that someone had already found, backfilled, and sealed with a large blocking stone at some earlier, unrecorded point in time.

The structure is a souterrain, a type of underground construction associated with early medieval settlement in Ireland, typically built of dry stone and used for storage, refuge, or both. This particular example sits at the western side of a ringfort, the circular earthwork enclosure, now largely levelled, within which it was originally built. O'Flanagan noted it in 1844, describing it simply as "subterranean chambers", which turned out to be accurate. When O'Kelly and Shee investigated the site in 1968, following the accidental breach, they found a roughly circular stone-built chamber about three metres in diameter and 2.6 metres high, roofed using corbelling, a technique in which stone courses are laid so that each projects slightly inward over the one below, eventually closing the space without a true arch. A low creepway, just half a metre in both height and width, connected this chamber to a stone-built passage running east to west, at least 4.5 metres long and wide enough to suggest it functioned as a second chamber rather than a simple corridor. Both ends of the passage tapered, the western wall and sides were corbelled to allow the use of short lintels across the top, and the eastern end was blocked, though probing indicated the structure continued further in that direction, its full extent still unknown.