That pairing is what makes the site at Bunalunn quietly interesting: each mill employed a distinct type of waterwheel, which suggests either a deliberate division of milling tasks or a phased development over time as technology or demand changed.

The larger of the two survives above ground as a three-bay, two-storey building with a slate roof, measuring roughly 12.4 metres along its main axis. Its wheelpit, set along the south-west gable and about 1.7 metres wide, housed an undershot waterwheel, the simpler of the two types, in which the current strikes the lower blades of the wheel and drives it forward by the force of flow alone. Only about three metres to the south-west, the foundations of a second, smaller mill remain. Its narrower wheelpit, just 1.4 metres wide and positioned along the north-east wall, was built for a breastshot waterwheel, a more efficient design in which water is delivered mid-height onto the wheel, combining the push of current with some of the weight of the water itself. Both mills retain what are described as lintelled tail races, the channels that carry spent water away from the wheel and back into the river, here finished with stone lintels across the outflow openings rather than left as open cuts.