The site goes by the name Kiltennan Fort, yet the structure itself is not a fort in any defensive sense. It is a cairn, a subcircular mound of earth and stone measuring roughly eighteen metres east to west and just under sixteen metres north to south, rising to between two and two and a half metres at its highest point. The name appears to have attached itself somewhat casually: the 1842 Ordnance Survey six-inch map does not mark any mound here at all, only a trigonometrical survey point labelled "Kiltennan Fort". It was not until the 1897 twenty-five-inch plan, and again on the 1920 edition of the six-inch map, that cartographers recorded the mound itself, labelling it simply "Carn".

The ridge it occupies is called Knockacarn, and the cairn sits on reclaimed pasture where the land falls away to the south-west, opening out wide views from east through south to west. Up close, the mound is regular and smoothly rounded, though noticeably steeper near its base on the northern, eastern, and southern sides, where the ground appears to have been cut back at some point. On the northern side, the base runs in an unusually straight edge for about seven and a half metres. There is also a slight hollow just to the south-east of the summit, the kind of detail that invites speculation but resists firm conclusions without excavation. What gives the broader landscape its particular texture is the company the cairn keeps: two raths, the circular earthwork enclosures associated with early medieval farmsteads, lie within roughly twelve metres and eighty metres to the east and east-north-east respectively, suggesting this corner of Kiltennan was a place of some sustained significance across different periods.