Brecon Road (B4520)
The B4520 is sixteen miles north from Brecon to Builth Wells up the Honddu valley: hedged, fast-flowing lanes with blind corners as far as Upper Chapel, then the hedges stop, the road widens and climbs onto the edge of Mynydd Epynt before the long fall into Builth. The curve score is only 4.4 but the elevation change is 520 m, so it is a road about crests and gradient rather than steering lock. Smooth tarmac; it rewards reading the blind summits and leaving room for what the hedges hide.
The upper half skirts the Sennybridge live-firing range and is open sheep ground, and the Plough and Harrow at Upper Chapel has closed, so there is no pub between Brecon and Builth. Farm exits drag mud onto the lower half after rain.