Video report by ITV Anglia's Stuart Leithes
The Holywell Ponds at Longthorpe on the outskirts of Peterborough are topped up by a constant flow of water that bubbles up at the site.
And a man made grotto, or 'folly', can also be found there - which has sparked rumours of a secret passage - and that people have lived there.
The ponds are now surrounded by a housing estate and kept locked by the council to discourage antisocial behaviour.
Monks have been thought to have used the ponds nearby for fishing hundreds of years ago.
But because the folly was not built until the mid 18th century, some stories cannot be true.