A souterrain is a man-made underground structure, typically associated with early medieval settlement in Ireland, used variously for storage, refuge, or concealment. This one, on gently sloping pastureland above the Anascaul Valley, was described as 'unusually extensive' when first recorded by Ashe in 1954, and the accessible portion alone suggests something more elaborate than most. What lies beyond the two surviving chambers is simply not known.

The accessible section is roughly L-shaped and consists of two rectangular chambers connected by a creepway, a low connecting passage just wide enough to squeeze through. The first chamber runs east to west, measuring 3.4 metres long and just over a metre high, its drystone walls corbelled inward at the upper courses so that the ceiling narrows to around 0.6 metres across. Seven flat slabs form the roof, and entry requires removing one of them entirely. A short creepway, only a metre long and less than half a metre wide, links this chamber to the second, which is at least two metres in length but blocked at its northern end by collapsed earth and stone. The debris spills back into the creepway itself, making the connection between the two chambers difficult to navigate. The walls of the second chamber combine upright standing slabs with drystone courses above, again slightly corbelled near the top, and four flat slabs close it overhead. Beyond this point the structure continues, but in what form and for how long, no survey has established. Locally the site goes by the name 'Ferriter's Fort', though there is no trace of any associated surface monument to explain the designation.

The site sits on open pastureland with a wide outlook north and west over the Anascaul Valley, which makes the approach relatively straightforward in clear conditions. The interior, where accessible at all, is very low, and the creepway between the two chambers is made more difficult still by the debris that has migrated into it over time. Anyone with a serious interest in early medieval underground structures will find it genuinely unusual, precisely because so much of it remains unexamined.