The tides at Castlecliff have recently exposed a possible WWII relic that is likely to have sat beneath the tarseal near Morgan St carpark for many years.
Local resident Lynne Douglas said she believes the structure is one of a number of pillbox guard posts that were built around the coast in 1942-44 in anticipation of a Japanese military invasion.
According to the Whanganui District Council archives, there were a total of 28 pillboxes built in Whanganui from 1942-44 and up to 18 of them were in Castlecliff.
"This one appears to have only been discovered now that the rubble covering it has fallen away," said Mrs Douglas.
"How did it get there?"
She has a long-held fascination with the pillboxes and has shared her enthusiasm with coastal scientist Dr Roger Shand.
Dr Shand and Mrs Douglas have previously spoken to the Chronicle about taking care of Whanganui's WWII defences and local engineer and researcher Karen Wrigglesworth also wrote about them last year.
She wrote that the New Zealand Home Guard numbered around 11,000 in 1942 but only 800 rifles were available.
The information came from a secret report published in 1942 and Mrs Wrigglesworth believes that the pillboxes may have been to boost morale rather than provide real defence if an enemy attack eventuated.
Most of the structures were of the arrowhead (T49) type with a central firing area and wings at either side for living quarters.
Mrs Wrigglesworth said she was keen to go and have a look at the newly-exposed structure.
"There was, understandably, quite a bit of secrecy around the building of the locations of the pillboxes when they were built," she said.
"It is exciting to think this might be one that no-one realised was there."
Mrs Douglas said she hopes that someone may have a recollection of a pillbox in that location.
"People who know about the stories are disappearing and the structures are an important part of Whanganui history," she said.
Having shared the news of her discovery with Dr Shand, Mrs Douglas said although he knows of other structures that are now submerged by sand or out at sea, he is not aware of one in that location.