Pontcysyllte Aqueduct

Thomas Telford and William Jessop finished this in 1805 and it has never needed replacing. A cast-iron trough, bolted together in sections and sealed at the joints with Welsh flannel and lead, carries the Llangollen Canal 307 metres across the Dee valley at a height of 38 metres. The towpath runs along one side behind a railing; on the other, the water comes right to the lip of the trough with nothing at all between it and the drop, which is why boaters describe the crossing as flying rather than sailing. Narrowboats still cross daily in season, and the canal runs on west to Llangollen and the Horseshoe Falls weir that feeds it.

What you actually see

• The crossing on foot - a towpath at trough level with an open drop on the far side.
• The trough - cast iron sections bolted and sealed, unchanged since 1805.
• Trevor Basin - the canal wharf and winding hole at the northern end.
• The valley below - the Dee, the river path and the 1848 railway viaduct alongside.

When to go

Boat trips run roughly Easter to October and the aqueduct is busiest on summer weekends, when the towpath becomes single file. The walk is open all year and free. Mornings give the calmest water in the trough and the cleanest reflections. Autumn colour in the Dee valley is the best backdrop; winter wind up there is bitter.

Honest expectations

The towpath is narrow and the unfenced side unnerves plenty of people, including some who turn back halfway across. There is no barrier at all on the water side. Parking at Trevor is charged and fills by mid-morning in summer. Boat trips are short for the price. Cyclists and walkers share a path built for neither.

Nearby

Llangollen, the Horseshoe Falls weir and the Chirk aqueduct and tunnel to the south.