The depression runs roughly thirteen metres in total, changing direction once, and three large flat stones sit half-buried within it, almost certainly the exposed lintels of a roofed underground passage. What lies below has not been entered in roughly three decades.

The structure is a souterrain, a type of underground chamber or tunnel built during the early medieval period, typically of drystone walling, meaning stones laid without mortar. Souterrains are found throughout Ireland, usually in association with ringforts, the circular enclosed settlements that were the dominant form of rural habitation from roughly the sixth to the twelfth centuries. Their exact purpose is still debated; cool storage, refuge, or concealment are the most commonly proposed explanations, and individual examples may have served more than one function. At Caherlissakill, the souterrain sits within the ringfort identified as GA071-014, and according to the landowner, the passage was still accessible within living memory. The interior, when it could be entered, was lined with drystone walling. The passage runs north-west to south-east for about seven metres before curving eastward for a further six, a bent alignment that is itself fairly typical of the form, possibly intended to restrict light or movement into the chamber.

What survives above ground now is largely a matter of vegetation and subsidence. The depression is overgrown, up to a metre deep, and two metres wide. The three visible roof stones give the clearest indication of the original construction, though how much of the passage below remains intact is unknown. The site rewards careful looking rather than casual passing.