The B172 crosses the foot of the Ards Peninsula in County Down. The road was originally unclassified but gained its number in the late 1920s.
The road starts on the A48 in the eastern suburbs of Newtownards and heads east along Movilla Road, which runs between housing estates. The road climbs and soon reaches open country. We cross the fields and follow a dead-straight road to a junction where we TOTSO right. There's a TOTSO left shortly afterwards, then we continue east along another straight road.
After passing beneath Ballycopeland Windmill the road starts to wind and then we enter Millisle. The road is residential, although we do also pass a large caravan park on the left. The road ends at a T-junction on the A2 coast road, although the sea is only just visible. The village centre is to the right.