It is the kind of feature that most people walk over without any awareness of what lies beneath, and yet it represents one of the more intimate details of early medieval Irish rural life to survive in the archaeological record.

A souterrain is an underground stone-lined passage or chamber, typically associated with ringforts, the circular enclosed farmsteads that dot the Irish countryside from the early medieval period. Their precise function is still debated, though storage of perishables in a cool, dark space and occasional refuge are the most commonly cited purposes. The example at Cush was uncovered during excavations of what the excavator called Ringfort 2, carried out between 1934 and 1935 by Seán P. Ó Ríordáin, whose findings were published in 1940. Ó Ríordáin recorded the passage as running from near the centre of the enclosure in a direction slightly south of east, measuring just over fourteen feet in length and averaging somewhat less than two feet in breadth. The western end had been cut into the clay at a slope, forming a ramp down from the surface into the passage itself. At the north-eastern corner, a scatter of stones was identified as the remnants of a ventilation shaft, a feature Ó Ríordáin noted was more fully preserved in other ringforts he examined at the same site. The shaft is a small but telling detail; it suggests these underground spaces were intended for more than momentary use.

Cush lies in east Limerick, and the broader site contains multiple ringforts in close proximity, which made it a particularly productive location for Ó Ríordáin's excavations. The souterrain itself is no longer accessible in any meaningful sense; what was exposed during the 1930s dig has long since been backfilled or weathered back into the landscape. For anyone visiting with an interest in the archaeology, the value lies less in seeing a visible structure and more in reading Ó Ríordáin's 1940 report alongside the topography. The Google Earth orthoimages compiled as part of the site record offer a useful way to orient oneself relative to the ringfort boundaries before visiting. The site repays patient attention rather than a quick look.