It is a togher, an ancient road built across wet or marshy ground, and the remarkable thing about this particular example is its simplicity. Just one compact layer of hazel brushwood, the individual stems no thicker than two or three centimetres, laid lengthways and pressed into the bog. The whole thing is only about one and a half metres wide and barely five centimetres deep, a structure so slight it seems more like a suggestion of movement than a road.

Toghers were a practical solution to a landscape that was otherwise impassable for much of the year. Builders would cut and lay brushwood, planks, or split timbers across the surface of a bog to create a stable footing, and Ireland's anaerobic, waterlogged peat has preserved many of them in extraordinary condition for hundreds or even thousands of years. This example at Derrynagran is classed as a type three togher, meaning it belongs to a category defined by its single-layer brushwood construction, in contrast to more elaborate examples that might use heavier timber or multiple laid courses. The hazel used here runs in a northwest to southeast orientation, suggesting a deliberate line of travel across the wetland rather than a casual scatter of material.