The rath at Tullymurrihy is not especially large, not dramatically sited, and not in particularly good repair, but it contains one of the more quietly intriguing features any ringfort can offer: a souterrain, an artificial underground chamber or tunnel typically built during the early medieval period, probably used for food storage or as a place of refuge. That it survives at all, given the state of the rest of the monument, is worth pausing over.

The fort itself is a circular raised area measuring 34 metres north to south, sitting on a break in a north-facing slope where the ground levels briefly before dropping away. It is defined by an earthen bank standing about 1.25 metres high, a modest but legible boundary that would once have enclosed a farmstead, most likely sometime between the sixth and twelfth centuries, when ringforts of this type were the dominant form of rural settlement across Ireland. Outside the bank there are traces of a shallow fosse, which is simply a defensive ditch, and beyond that a concentric field fence runs roughly six metres further out, suggesting the enclosure once had a more layered boundary than survives today. The souterrain is in the northern part of the interior, and the fosse and the ground inside the bank have been used as a rubbish dump, which is not unusual for monuments that have passed out of living memory and into agricultural inconvenience.

The site sits in pasture, which means the earthworks are visible as grassy undulations rather than exposed stonework or excavated trenches. The bank is low enough to be easy to miss at distance, but at closer range the circular logic of the place becomes apparent, the way the raised ground describes its own edge. The souterrain opening is on the north side of the interior, though underground passages of this kind are typically partially collapsed or sealed and should not be entered.