This is a cashel, a type of stone-built ringfort, though here the distinction between deliberate construction and natural topography has grown difficult to read. The enclosing bank, just two and a half metres wide and no more than seventy centimetres high on the interior, is so reduced along its eastern and northern arc that it becomes discontinuous, barely a suggestion of a boundary rather than any kind of defensive statement.

Ringforts, of which thousands survive across Ireland in varying states of preservation, were the typical farmstead enclosures of the early medieval period, roughly the fifth to twelfth centuries. A cashel is simply a ringfort whose enclosing wall was built primarily of stone rather than earthen bank and ditch. At Lugnagall, the fosse, the external ditch that typically accompanies such enclosures, is no longer visible at ground level, though whether it was never dug, has silted and grassed over, or was never part of this particular design is hard to say from surface evidence alone. What does remain is a slight raising of the enclosed oval ground, measuring thirty-three metres on its longer north-east to south-west axis and nineteen metres across, and a gap of just under two metres in the bank to the north-east that is a plausible candidate for the original entrance.