A souterrain, meaning an artificially constructed underground passage or chamber complex, typically associated with early medieval settlement in Ireland, this one runs to roughly 33 metres in total extent and comprises eight chambers connected by a series of narrow, often tortuous passages. It is the most extensive souterrain recorded on the Dingle Peninsula, and its sheer complexity raises questions that have not yet been fully answered.

The structure begins with two drystone-built chambers, the first entered through a gap barely 63 centimetres wide and 37 centimetres high, which then give way to a largely rock-cut interior tunnelled directly through bedrock and subsoil. The passages between chambers are frequently so narrow, at points only 35 centimetres wide, that passing through them requires considerable effort. Chamber five is currently a dead end, though whether this was always intended is unclear. The blocked ends of several tunnelled chambers may reflect later collapse, but they may equally mark the sites of original construction shafts, pits sunk to allow the excavated spoil to be removed upwards rather than dragged back through the entrance. If so, those pits were subsequently walled off and infilled, leaving no trace above ground. The site has other unresolved details. Writing in 1893, a researcher named Deane recorded that a skull and other bones had been found in chambers four and seven, and a writer named Champneys, in 1910, mentioned two bodies discovered in a sitting position in what he described as a very elaborate souterrain near Ventry, almost certainly the same remains. Separately, when the present landowner's father was drawing stones from the ringfort, a small slab-lined grave came to light containing an iron box of coins, though the details of that find remain sparse.