The B4574 is a V-shaped road in east Cardiganshire. It serves – but does not reach – the village of Cmwystwyth. The road was originally unclassified but gained its number in 1935.
The route starts on the A4120 at Devil's Bridge, immediately south of that road's eponymous bridge over the Afon Mynach. The road follows the river upstream, climbing as it does so; there is no space in the valley bottom for the road. To begin with the road runs through a wood but soon enters open country, with a good view over the valley to the left. We enter another wood and pass a masonry arch (built in 1810 to celebrate the jubilee of George III) which marks the summit; the road used to run through this but as that caused a bottleneck a small cutting was built in the 2000s and we pass to its right.
The road now descends and crosses a narrow bridge over a small stream before going over a ridge and reaching the valley of the Afon Ystwyth. There's a very sharp TOTSO to the right; the unclassified road ahead runs up the valley through Cwmystwyth then over the hills to Rhayader. Owing to the route of the B4574 very few vehicles would need to take this turn anyway.
Now heading west, we recross the narrow stream mentioned in the last paragraph and then pass through Hafod, where the church is virtually the only building. The road continues to wind for about another mile before a steep descent leads to a T-junction on the B4343, which has got here from Devil's Bridge by a shorter way.