You hear it before you understand it: water running in an iron trough thirty-eight metres above the River Dee, on stone piers so slender they look drawn rather than built. Thomas Telford and William Jessop finished the Pontcysyllte Aqueduct in 1805 to carry what is now the Llangollen Canal across the valley, and more than two centuries later narrowboats still glide over it, steered by people trying very hard not to look down. There is a towpath on one side with railings; on the other side there is only the edge of the trough and air. Walk across if you have a head for heights. It is one of the strangest and best ten minutes in Wales.
The aqueduct belongs to a whole engineered landscape. A few miles south, Chirk has its own aqueduct with a railway viaduct right alongside, and upstream the canal is fed from the Dee at the Horseshoe Falls, which is a curved weir rather than a waterfall but beautiful all the same. Telford also built the A5 through here, the London to Holyhead road, with gradients gentle enough for mail coaches, and you can feel his hand in the way it flows along the valley.
For riders the real magnet is a few miles up the valley at Llangollen. From the town the A542 climbs the Horseshoe Pass, a proper set of bends looping up a bare hillside to the café at the top, a well-known meeting place for bikers on any dry weekend. Beyond it the road drops towards Ruthin and the Clwydian hills. Alternatively the B5605 and the lanes around Ruabon and Rhosllanerchrugog take you through old coal country, where terraced villages and chapels sit on the slopes. In wet weather watch for slick slate chippings and farm mud; in summer the A5 through Llangollen can crawl behind caravans.
Trevor Basin, at the north end of the aqueduct, has parking, a café and a pub, and it is where you will start the walk across. Fuel is easy in Ruabon, Chirk and Llangollen, and Rhosllanerchrugog has the full range of shops. Llangollen itself is a good lunch town, with the Dee crashing over rocks right under the bridge and the ruins of Castell Dinas Brân on the hill above, a steep walk that pays you back with the whole valley at your feet.