At the southern end of the A487 Cardigan bypass, just half a mile from the western end of the A484, there is a roundabout at a place marked Pentwyd Isaf on the map. Here is, of course, the A487 western coastal route, together with the B4546 leading towards Poppit Sands on the Teifi estuary, as well as the start (or depending on your point of view, the finish) of the Pembrokeshire Coastal path. If you don't fancy walking, the other road at the roundabout is the A478, and it will take you by a more direct route to Tenby, not far from the south eastern end of the path.
Cardigan - Tenby
We head south from Cardigan, skirting the lower slopes of a hill, towards Pen-y-bryn, where a left turn along an unclassified road will take you to the village of Cilgerran, complete with its ruined castle, perched high on a cliff overlooking the River Teifi, where you might just see a coracle on the river. But Cilgerrna isn't on the A478 so we must retrace our steps to continue southwards, the road gradually gaining in altitude to around 600 ft at its junction with the B4332 near Boncath.
As we approach the village of Crymych, the road becomes steeper, reflecting the fact that we are now on the eastern fringe of the Preseli Mountains, the source of some of the stones used at Stonehenge. Although we are now as far inland as we will get, this section of the road forms the boundary of the Pembrokeshire Coast National Park - the reason for this is that the park includes much of the Preseli hills. After leaving the park boundary, the road rises to a crest where there is a viewpoint over the hills to the west.
The next section of road begins to descend again, falling away gently to the west, before a steeper slope into the Eastern Cleddau Valley, though this is too far away to see from the road. We then pass through Llandissilio, which is as big a place as any passed so far along this road (but not very big - this is a typical west-Wales rural A-road!)
At Clunderwen we cross the main London to Fishguard railway, and the village is considered important enough to have a station. A couple of miles further south, we cross the A40 London to Fishguard trunk road, to the north east of Narbeth, a small town - also with railway station and castle. We enter Narbeth by turning right at a sharp bend - the straight on option takes traffic along the B4314 towards Red Roses, along what was once the A40.
On the A478 looking down into Templeton
We continue south through Templeton, where we meet the Carmarthen to Tenby railway line (the same one that serves Narbett), which runs parallel to us through to Kilgetty, where we cross the A477 to the south-west of the town - both the A477 and A478 bypass the town centre. As we have travelled south from the A40, so the road has become progressively busier, as we pass more and more signs of civilisation. At Kilgetty we pick up all the tourist traffic heading towards Tenby, gaining primary status in the process. Almost immediately we pass a left turn to the B4316, which leads to Saundersfoot, a pleasant village with a large harbour, which largely caters for tourists.
The A478 loops round and then under the railway line, then once again forms the boundary of the National Park, but this time the western boundary! We reach another roundabout, where we again have the opportunity to join the B4316 towards Saundersfoot, or to follow the old A478 through New Hedges. The A478 now bypasses New Hedges before we reach Tenby itself. We enter the town and get a good view of a railway viaduct, where the A4218 gives one route to the town centre. The A478 enters alongside North Beach, terminating on the harbourside by the town wall.