A togher is a timber trackway, typically laid across wetland to allow people and animals to cross terrain that would otherwise be impassable, and the one at Derrindiff is among the more substantial examples on record. What makes it particularly arresting is a detail that has never been satisfactorily explained: at one point along its length, a deliberate pattern of triangular wedges was cut into the upper surface of the oak planking. Whoever made them knew exactly what they were doing, but their purpose remains unknown.

Dendrochronology, the science of dating timber by its growth rings, placed the construction of the togher to 1612 plus or minus nine years BC, a precision that feels almost unsettling given the age involved. The road was built in two layers. A substructure of longitudinal and transverse roundwood, essentially small trimmed poles laid in opposing directions for stability, was topped by a superstructure of half-split oak planks running lengthwise along the track. These planks were held in place by obliquely set pegs driven into the ground on either side, and some timbers had morticed ends, meaning joints had been cut into them to lock components together, a sign of considered carpentry rather than improvised construction. One individual timber measured at least fifteen metres in length. When examined during excavation, the togher ran WNW to ESE, shifting slightly to NW-SE towards one end, and reached a minimum width of four metres.

When inspected in 1999, the togher was still visible across nineteen fields for a distance of 385 metres, surfacing in drain faces and, in places, sitting exposed at field level where agricultural milling had begun to disturb it. At one point the oak planking appeared at a depth of just over a metre in the base of a drain, the wide planks, some nearly one and a half metres across, still resting on their roundwood substructure after three and a half millennia in the bog. The preservation that the anaerobic, oxygen-poor conditions of wetland provide is what allows such detail to survive, and what makes the unresolved question of those cut triangles all the more tantalising.