|Length:||3.8 miles (6.1 km)|
|Meets:||Unclassified, B4334, A487|
|Route outline (key)|
The B4321 is a short narrow B-road heading inland from the Cardiganshire coast. It was originally unclassified but gained its number in 1935.
The road starts alongside the beach car park in Llangrannog and then climbs through the narrow streets of the village, meeting the B4334 near the church; the road past the churchyard is barely wide enough for a single vehicle. After the village apparently ends there are still a number of buildings passed by the road; along with the trees and hedges this means the road does not enter open country for some time. There's a brief S2 section at a road junction then the road widens as it comes in sight of open fields; this doesn't last long as the central line has gone again by the time we reach Pontgarreg.
The road climbs steeply out of the scattered settlement and briefly becomes S2 again at a hairpin. A narrow country lane is now followed and the central line comes back after about half a mile; again it doesn't last long. We continue on past a caravan park to end at a crossroads on the A487 in Pentregât.