This article is about the Class III road numbered C321 maintained by DfI Roads. For other roads numbered C321, see C321.
The C321 starts on the B25 in Rostrevor and makes its way into the countryside to the east, crossing the Kilbroney River as it does so. From here the road runs in a generally north east direction up the valley, crossing the river once more further upstream. The road reaches its high point as it passes between Tievedockaragh and Crotlieve Mountain. Down the other side, the road crosses the Upper Bann just before meeting the B27. The road crosses the B27 and ends on the B180 just a short distance to the north.