The cartographers who recorded it in that first survey drew a small rectangle of around six metres by five metres alongside a circle roughly four metres across, a plan that corresponds loosely with the entrance arrangements still visible today.

The accessible section of the souterrain consists of three drystone-built rectangular chambers arranged in a rough L-shape. The first chamber, about 5.6 metres long and 1.2 metres wide, runs roughly north-northwest to south-southeast and is entered through a modern breach at its southern end. At its far end, a creep, the low, narrow connecting passage that is a characteristic feature of Irish souterrains, just 0.76 metres wide, leads through to a second chamber measuring around 3.6 metres in length and one metre in width. Beyond that, a third and longer chamber, some 10.5 metres in total, branches off at almost a right angle, running on a north-northeast to south-southwest axis and entered through a separate breach at its south-southwestern end. It is likely the three chambers were originally connected in a continuous sequence, but collapse at the right-angled junction has obscured whatever passage or creep once linked them. The third edition Ordnance Survey map, published in 1915, shows two dots about ten metres apart, probably marking these two separate breach points, by which time the collapse may already have been an established fact.

The souterrain sits within the graveyard at Lattoon, and the long third chamber still has its northwestern end filled with soil, which may conceal further extent or simply reflect centuries of gradual subsidence. The chambers are drystone built, meaning no mortar was used, the stones relying entirely on their own weight and careful placement for stability, a construction method that, when left undisturbed, can survive underground for over a thousand years.