The evidence for it is slight but oddly compelling: a landowner's childhood memory of dropping stones through a gap and hearing them fall, and a nineteenth-century record describing a cavern on the same spot.

The site sits within a rath, the Irish term for a roughly circular earthen enclosure, typically dating from the early medieval period and used as a farmstead. Raths are common across Ireland, but the underground chambers sometimes found within them, known as souterrains, are rather more unusual. A souterrain is a man-made passage or chamber built from stone, usually associated with storage or refuge. At Caherdean, the earliest written reference to such a feature appears in the Ordnance Survey Name Books from the 1840s, which noted a cavern within this particular rath. When surveyors visited the site in more recent times, the landowner led them to two large stone slabs lying in a clear area in the northern half of the enclosure. He identified these as marking the likely entrance or roof of the old cavity, drawing on a memory from his own childhood of peering into a gap beneath the slabs and tossing stones down into the darkness below. By the time of that inspection, however, the cavity itself was no longer visible at the surface.

What remains, then, is a place defined largely by absence: a possible chamber that has not been excavated, not been confirmed, and not been seen for decades. The slabs are there. The childhood memory is there. The 1840s record is there. Whether the hollow beneath them still exists, or has collapsed and filled over the years, is a question the ground has not yet answered.