The one at Lettercannon, tucked into a hollow on a west-facing slope in south-west Kerry, breaks that convention entirely. Its outline is triangular, an unusual geometry that owes as much to the local landscape as to any builder's intention.

The structure makes clever use of what was already there. A natural rock scarp along the southern edge, stretching nearly eighteen metres, forms one side of the triangle and would have required no construction at all. From that rocky baseline, a drystone wall, built without mortar in the traditional manner, runs northward along the western side for just over ten metres, standing roughly a metre and a quarter high and half a metre thick. A slightly curving wall then completes the enclosure by sweeping from the north end of that western wall back around to meet the scarp at the south. The entrance, just under a metre wide, sits at the southern end of this curving wall and is marked by a large boulder on its southern side, a modest but deliberate threshold. A small stream, flowing westward, skirts the outside of the northern wall, and may have been one reason this particular hollow was chosen in the first place.

What the enclosure was used for is not recorded. Enclosures of this kind in Kerry served a range of purposes across different periods, from stock management to habitation to more ceremonial functions, and the triangular form here, shaped partly by accident of geology, makes direct comparison with other sites difficult. It sits in rough pasture still, unexcavated and largely undisturbed, its drystone walls holding their shape in the hollow where they were built.