Some say it was brought back by a merchant seaman in the 19th century and is how a nearby pub got its name.
Others believe a former school student donated it as a testament to an inspirational teacher.
But the true origin of whale bone archway at Sewell Park Academy in Norwich remains a mystery to this day.
Now, ex-pupil Wendy Cocks has made it her mission to find out more about the unusual structure, which appears to be made from a whale's jaw.
The 70-year-old, from Mile Cross, attended the school from 1958 to 1962, when it was known as Blyth Grammar School for Girls.
She said: 'I can remember the whale bone arch, but no one ever said how, where or why it got there.
'On Facebook, no one seemed to know what it was, and when I went onto Wikipedia, the only information was from 12 years ago.
'I found it fascinating because we are getting all these ideas about its origin, but no one has come up with a definitive answer.'
Today, the unusual structure is hidden away from the public – and pupils – within the school grounds off St Clements Hill, north of the city.
Mike Lorenz, owner of the nearby Whalebone Freehouse, believes his pub's name is associated with the arch.
He said when he took on the pub in 1994, he was told the whale bone had been donated by a merchant seaman in the 19th century.
Mr Lorenz said: 'I was told he erected it at the gates to Sewell Park, but once it started to deteriorate it was moved to the school area.
'I can't think there would be any other reason why the pub got its name.'
The freehouse dates back to 1830, and records show that in 1865 it was known as the Whalebone Brewery.
Other theories about the arch's origin have appeared on a Wikipedia page from 2006.
A short caption under a photograph of the archway suggests it was a gift to the Blyth grammar school from a former pupil 'who found it washed up on a beach'.
The caption claims it was a 'testament to an inspirational geography teacher, Miss Mary Keele.'
Records show that the school dates back to at least 1890.
Do you know more about the arch's history? Email luke.powell@archant.co.uk
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