It is a burnt mound, a type of prehistoric feature found widely across Ireland and Britain, and the leading theory about what these sites represent is, to put it mildly, unglamorous: they are thought to be the debris from repeated episodes of heating stones in a fire and dropping them into a water-filled trough to bring it to the boil. Whether for cooking, bathing, or some other purpose involving hot water, the cracked and discarded stones built up over time into exactly the kind of low, slightly curved mound visible here. This one is roughly D-shaped in plan, about 4.8 metres north to south and 11.6 metres along its straight southern edge, rising to around 1.25 metres at its highest point.

What makes the spot on Tooreennamna notable is not the mound alone but its immediate company. Around thirty metres to the north-west stand a standing stone and a boulder-burial, a boulder-burial being a form of prehistoric funerary monument in which a large capstone rests on smaller supporting stones, typically covering a burial deposit beneath. The clustering of a burnt mound with a standing stone and a funerary monument in such close proximity points to this hillside having been a place of repeated, perhaps sustained, prehistoric activity. Whether these features were used at the same time, or whether one drew later people back to a spot already marked by an earlier structure, the notes do not say, and the archaeology has not yet given a clear answer. Gorse bushes and loose stones now occupy part of the mound's western sector, softening its outline and making it easy to overlook against the rough pasture around it.