The B175 is a winding road in central County Down. It was originally unclassified but gained its number in the late 1920s.
The road starts on the A24 on the southern edge of Ballynahinch and heads south along Spa Road. To begin with the road is lined with hedges but we climb through a cutting and shortly come in sight of open fields. We soon reach the village of Spa, where there's a TOTSO left at a crossroads by the Presbyterian Church and then we climb out of town.
McAuley's Lake soon comes into view on the right of the road and we run along the shore for a distance before continuing across the fields to the south. After an unexpected row of houses on the right there's a TOTSO right, then a TOTSO left shortly afterwards so we avoid Drumaroad. Presently a T-junction is reached, where we TOTSO right to go over the Moneyarragh River, then take the next left turn to continue south. The straight road here is narrow and only becomes S2 when part of the B175.
We continue across undulating fields with the hills around Castlewellan in the distance. We bear left to avoid the climb, however, instead descending to the south into the valley of the Ballybannan River and enter Annsborough. We end here at a T-junction on the A25.