It is a togher, an ancient trackway of the kind laid across waterlogged or marshy ground to allow people and animals to cross terrain that would otherwise swallow them whole. The preservation of organic material in Irish bogs has meant that many of these structures survive in extraordinary condition, and the Derrynagran example is a quiet illustration of how much practical engineering knowledge existed long before written records.

This particular togher runs east to west and measures fifteen metres in length, just under three metres wide, and roughly fifteen centimetres deep. Its construction follows a straightforward but effective logic: a single layer of birch roundwood, the individual pieces reaching up to about sixteen centimetres in diameter, laid lengthways along the direction of travel and interspersed with brushwood to fill the gaps and distribute weight more evenly across the soft ground beneath. The use of birch is notable; it is a fast-growing, relatively light timber, well suited to this kind of temporary or semi-permanent infrastructure. The brushwood woven between the roundwood would have added friction and stability underfoot, making the surface usable even when wet. Toghers like this one are classified by archaeologists according to their construction method, and a class 3 designation refers specifically to this longitudinal roundwood technique, distinguishing it from plank roads, transverse log roads, and other variants found across Irish wetlands.