The legendary Newsround presenter, 84, left it to be petrified 20 years ago.
The ancient process involves dripping water on clothing.
The Countryfile host then returned to Mother Shipton’s Cave to see what it was like.
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His sock is now rock hard after two decades at the tourist attraction in Knaresborough, near Harrogate, North Yorkshire.
It is set to feature on Countryfile on Sunday (17 Aug).
Jay Stelling, marketing co-ordinator at Mother Shipton’s Cave, said: “It was so great to meet John Craven.
“And to discuss the history of the site with him. He’s a real icon.
“We work so hard to keep this ancient site alive, and to continue to share the magic.
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“So it will be so rewarding to see it feature on this show for more people to learn about who Mother Shipton was.”
Craven’s sock is on display in the Cabinets of Curiosities at Mother Shipton’s Cave, along with various items donated by celebrities over the years.
Socks owned by comedian Bobby Davro and TV presenter Jake Humphrey now look centuries old.
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“A hat worn by movie legend John Wayne is also on display at the museum.
Supermodel Jodie Kidd handed in a woollen glove while Julie Bradbury donated earmuffs.
A Korean soldier’s hat from the James Bond film Die Another Day, David Suchet’s hat, stiletto shoes worn by Raquel, played by Sarah Lancashire in Corrie, and an Ewok donated by Warwick Davis also feature.
Seth Armstrong’s trademark hat from Emmerdale and Agatha Christie’s handbag also feature. The most historic and valuable item is a shoe left by Queen Mary when she visited in 1923, as reported on What’s The Jam.
Chat show king Jonathan Ross left a pair of his bright orange boxer shorts there three years ago, and they now look ancient.
In the Middle Ages, people believed that the Petrifying Well in Knaresborough was connected to the devil and that they would be turned to stone if they came too close.
Later, people believed it had miraculous healing powers and used to carry their sick and dying relatives to bathe in the well pool and drink the water.
The well was first recorded by Henry VIII’s antiquary, John Leland, in 1538. It opened to the public in 1630.
Mother Shipton – real name Ursula Sonthell – was born in a cave next to the well in 1488.
She started having visions when she was older and predicted the Great Fire of London.
She was known as a witch and made a living telling the future. She died in 1561, aged 73.
Jay added: “We now know that the process is a natural phenomenon due to the high mineral content of the water.
“Compared to a stalactite or stalagmite, the items petrify very quickly. A small teddy bear takes three to five months, while larger porous items can take six to 12 months.
“It can take two years to get a good half-inch crust on non-porous items.
“In the old days, they used to hang everything from dead animals to wigs under the waters.”
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