Walking the watery plank

An impossibly narrow shimmery pencil line of water stretches out across the sky. Even the presence of a few tourists on the towpath cannot stop me catching my breath and giving a gulp of anticiption before setting off across the Pontcysyllte Aqueduct.
It's ludicrously narrow - inches wider than the boat and on the non-towpath side the water laps a foot below the top of the iron trough we're travelling along and were I to take a small step sideways from the helm, there isn't the merest thread of a guardrail to separate me from the 126 feet drop to the Dee Valley below.
Along the 1000 ft aqueduct I gaze down at a football pitch below, a sewage works on the other, the wide, rushing River Dee and off to either side at the wonderful, distant views.
What an engineering masterpiece this is. We're travelling on a structure build over 200 years ago, in sections of cast iron trough joined together with seals that still don't leak and build under Thomas Telford's direction in just ten years by manual labour alone under the gaze of people who said it could never be done.
An unforgettable experience!