A 200-year-old engineering masterpiece is going under the microscope for a vital inspection.

Chirk Tunnel, of one of the centrepieces of the 11-mile Llangollen Canal World Heritage Site designed by Thomas Telford, will be checked out by Canal and River Trust workers.

The trust has the challenging task of maintaining a 2,000 mile canal network which was largely constructed during the reign of George III (1760 to 1820).

The Llangollen Canal is currently one of the busiest and most popular waterways in the country and keeping its iconic structures, like Chirk and Whitehouse tunnels and the Pontcysyllte Aqueduct, in good working order requires regular maintenance.

Tomorrow, the Canal and River Trust engineering specialists will use a boat to travel through the 421 metre-long Chirk tunnel and the 174m Whitehouse tunnel to assess any structural changes that have occurred since the last principal inspection three years ago, including checks for leaks, cracks and damaged brick work.

Their observations will then be analysed to decide if any major repairs are needed.

The tunnel contains more than a million bricks, with much of the surface sealed in clay to make it waterproof.

Opened in 1805, Chirk tunnel is the longest of three canal tunnels on the Llangollen Canal, formerly a branch of the Ellesmere Canal, and is remarkable as one of the first tunnels to incorporate a horse towing path.

Previously boat owners would have had to ‘leg it’ through a canal tunnel by lying on the roof of their vessels and effectively walking along the roof.

Chris Reynard, from the Canal and River Trust, said: “A trip into the canal tunnel is like stepping back in time.

“It’s dark, quiet, a little bit eerie and much of the brickwork dates back to when the tunnel was constructed two centuries ago.

“The Llangollen Canal is arguably more popular than ever before and our inspection is a good example of the type of work needed to keep it in top shape.”

For more information about how to support the work of the Canal and River Trust by donating or becoming a ‘Friend’, go to www.canalrivertrust.org.uk or call the customer services team on 0303 040 4040.