|Length:||8 miles (12.9 km)|
|Meets:||A539, B5103, A5104, A525|
|Route outline (key)|
It starts at an end-on junction with the A539 at the northern end of the Dee Bridge in Llangollen town centre. The westbound A539 has a TOTSO here and continues across the bridge to meet the A5 on the other side of the town. For about a mile the A542 closely parallels the top end of the Llangollen Canal, which terminates further west at Horseshoe Falls, a feature that actually is a man-made, horseshoe-shaped weir built by Thomas Telford to supply the canal with water.
The road leaves the valley of the Dee and starts to climb steadily upwards, passing the ruins of Valle Crucis Abbey on the right. It then traverses the highly scenic and surprisingly bleak Horseshoe Pass, at the top of which is the splendidly-named Ponderosa Café. The summit of the pass is 1387 feet above sea level, and there are magnificent views back down the valley towards Llangollen. It is not clear whether the name of the pass does come from the fact that the road follows a horseshoe-shaped bend in climbing up from Llangollen but this is the most likely definition.
Descending on the other side, the A542 enters more gentle country around the headwaters of the River Alyn. It crosses the A5104 at a roundabout, and about a mile later ends on the A525 at an acutely angled T-junction. The onward route to Ruthin from here along the A525 passes through the Nant-y-Garth Pass, a steep, twisty wooded defile about three miles in length.