The B4573 runs north of Harlech following a loop off the A496 along the edge of the coastal plain.
Starting on the southern edge of Harlech on the A496 the road heads north along Ffordd Isaf, signposted to the town centre. We follow a winding and surprisingly narrow road, with the sea sometimes visible to the left. After bearing round to the right we follow the High Street, which itself bears left then right to pass to the east of the castle, which is hidden behind the shops. We are quite high above the sea here; indeed, Ffordd Pen Lech, a side road, has a signed 40% descent.
After leaving town the road becomes wooded and it descends gently onto the coastal marsh. We leave the wood on reaching what is just above sea level, although as we're quite far inland here the sea is not visible. We continue on, with flat land to the left and a steep hill to the right - usually immediately to the right - before crossing a small stream and bearing left. We continue on into Glan-y-wern, where the A496 comes in from the left and TOTSOs, taking on the road ahead.
The Harlech area in 1961, showing the original routes of the roads north
The B4573 came into existence when a previously unclassified road gained its number in 1935. However, rather than following its present route it took a flatter line across Morfa Harlech along what is now the A496, with the exception that it went through Harlech along Tryfar (although it was diverted onto Ffordd Newydd in the 1950s).
At some time around 1975 the B4573 and the A496 swapped routes between Harlech and Glan-y-wern, the A496 taking over the B4573's former lowland route between these points while the old main road, hugging the base of the hills, became the B4573.