|Distance:||5.8 miles (9.3 km)|
|Meets:||A541, A5026, B5432, A5026, A548|
|Route outline (key)|
The B5121 is a largely rural B-road in Flintshire.
It starts on the A541 to the north of Nannerch. It heads north and quickly climbs steeply out of the valley it started in. After going through the long village of Lixwm it continues across undulating farmland before going through Brynford. It then descends the winding Brynford Hill, going under the A55 in the process.
The road crosses the A5026 Holywell bypass at traffic lights before reaching the town centre and another branch of the A5026. There is a multiplex west along this road, starting with a one-way loop round the bus station. Originally the B5121 started in Holywell (on the then-A55) and headed north; it was extended south to Nannerch in 1935.
The B5121 regains its number by turning north off the A5026. It passes St Winefride's Well (the holy well the town is named after) before continuing northeastwards along a road that never actually becomes totally rural. The road enters Greenfield and continues on with the sea just visible. It ends at traffic lights on the A548.