Barely thirty centimetres deep in places and just over a metre wide, it is easy to walk past without a second thought, yet its proportions, running nearly eleven metres along its main axis and a further eight or so along a shorter arm, suggest something considerably more deliberate than a natural hollow or a drainage ditch.

The depression sits within the north-western sector of a rath, the term for a ringfort, one of the circular earthwork enclosures built across Ireland during the early medieval period, roughly between the fifth and twelfth centuries, and typically used as a defended farmstead. Inside or alongside such enclosures, it was not unusual to find a souterrain, an artificially constructed underground chamber or series of passages, usually built from stone and roofed with lintels. Souterrains served various purposes, most likely for cool storage of dairy produce and, in times of threat, as a refuge or escape route. The one at Rappareehill appears to have collapsed at some point, leaving only the telltale L-shaped scar in the earth where the roof gave way and the ground above settled into the void below. The main axis runs roughly east-north-east to west-south-west, with the shorter arm branching off near the eastern end and turning towards the north-north-west, a configuration that matches the angled plans seen in souterrains recorded elsewhere in Ireland.