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This fascinating footage shows a lost underground tunnel hidden in Cardiff’s city centre.

Simon Fenoulhet believes that the tunnel may be related to a 13th century friary that once stood where the city centre is now.

He is reluctant to reveal its precise location, although he said it is in the Greyfrairs Road area.

Mr Fenoulhet, one of the Cardiff Contemporary festival’s artists in residence, has embarked on exploring the parts of Cardiff not normally seen above ground.

The artist is aiming to create an alternative map of the city linked to markers above ground for people on the streets to discover what lies beneath their feet.

Mr Fenoulhet had read about a tunnel along the banks of Cardiff’s feeder canal in an article on WalesOnline.

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In the piece, city historian Brian Lee wrote that as children he and his friends “would often venture a few yards inside but didn’t chance going any further”.

A book, called Cardiff Castle, which was published in 1923, spoke of a passage “discovered on the south bank of the Dock Feeder where it passes through the Greyfriars enclosure. The opening passage is 2ft 3in wide and on entering it, a tunnel runs westward towards the castle”.

Last week Mr Fenoulhet, who lives in Cardiff, went out hunting for clues to back up some of the rumoured underground locations in Cardiff – and in the process found some barely visible stonework.

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After arranging access, Mr Fenoulhet wriggled down inside and found a tunnel at about crawling height.

He later returned with experienced caver Vaisey Bramley for moral support and back-up.

The artist wrote on his Facebook page: “We went right to the end where there is a pile of earth from an earlier collapse followed by another a few metres on which blocked our way.

“It was a crawl until after the first pile of earth and then the last section was deeper which was a relief as it meant we could turn around rather than reverse out.”

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He reckoned that the rest of the tunnel “is silted up and could be dug out. How far it goes in total is a mystery.”

He said: “I think the archeologists should take a look at it before anything else happens.

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“I was prepared for disappointment but I was quite surprised when I saw that there was quite a lot intact. It runs underneath well known buildings in the city centre,” he said.

“I’m quite excited to see how far it would go but I think that’s a bigger job to make sure that its safe”.

Cardiff Contemporary is the largest visual arts festival Cardiff has ever organised. It runs until November 9. For more information visit www.cardiffcontemporary.co.uk