No earthwork rises from the ground, no stones mark its edge; the structure exists, to the casual observer, not at all. What gives it away is a cropmark, the faint but readable difference in how crops or grasses grow over buried features. Where a buried ditch or bank alters the soil's drainage and nutrients, the vegetation above responds differently, and from the air, during the right conditions, a pattern emerges that the ground-level eye simply cannot register.

The enclosure at Tullylusk was captured in aerial photographs taken by Michael Moore on 16 July 2006, a summer date that is no coincidence. Cropmarks are most legible during dry spells in late June and July, when moisture stress causes vegetation over shallower or disturbed soils to ripen or yellow faster than the surrounding growth. On that day, the circular form showed clearly enough to be recorded. Circular enclosures of this kind are found widely across Ireland and can date from the prehistoric period through to the early medieval, when they often served as the enclosing boundaries of a farmstead or small settlement, a form sometimes called a rath or ringfort. Without excavation, it is not possible to say with any certainty what period this particular example belongs to, or what it once enclosed.