It does not appear as a raised bank or a worn track but as a cropmark, the kind of subtle discolouration in growing grain or grass that reveals buried features to anyone looking down from the right height at the right moment. In this case, that moment came on 17 July 1967, when an aerial photograph captured two parallel fosses, that is, ditches or shallow trenches, running roughly northwest to southwest for approximately fifty metres. The feature sits south of a castle and southeast of an enclosure, and it is from neither the ground nor any standing structure that it can be appreciated, but from the sky, and from a photograph now more than half a century old.

Cropmarks form when buried ditches, walls, or disturbed soil affect the moisture and nutrients available to plants growing above them. Over a filled-in ditch, crops tend to grow taller and greener; over buried stone, they may be stunted and pale. Seen from above in the right season, these differences in growth trace the outlines of structures long since gone. The two parallel fosses at Castlekelly fit the pattern of a bounded roadway or track, the kind that would have served a castle or a nearby enclosed settlement. Whether it functioned as an approach road to the castle, a route connecting the castle to the adjacent enclosure, or something else entirely, is not known. The association with one or both features seems likely, but the photograph alone cannot settle the question.