That kind of deflection is rarely accidental. Boundaries tend to bend around things that were already there, things considered fixed or significant enough to route around rather than through, and this one has apparently been accommodating a pile of stones for a very long time.

The cairn itself is oval in plan, measuring roughly ten metres east to west and seven and a half metres north to south, and rising to about a metre in height. It sits slightly below and to the north-west of the Lugnagun summit. A cairn of this type is essentially a mound of gathered stones, often raised over a burial during the Bronze Age, though not always. What makes this one particularly interesting is the detail at its centre, or just west of it: two small stone slabs set at right angles to one another, which may be the surviving elements of a cist. A cist is a small stone-lined box burial, typically constructed to hold human remains along with grave goods, and when one survives at all it usually does so only in fragments, with the covering slab and much of the structure long since disturbed or removed. Whether these two slabs represent a cist in any complete sense, or simply what remains after centuries of disturbance, is an open question.