Royston Cave

History of Royston Cave

Scheduled Monument

The Royston Cave is a remarkable man-made feature without parallel, in structural terms, either in England or in Western Europe. … Although used in the medieval period, the cave was evidently sealed up and its existence remained unknown until 1742 when workmen erecting a bench for the butter market in the Mercat House (since demolished) discovered a millstone closing the entrance to a narrow vertical shaft. 

https://historicengland.org.uk/listing/the-list/list-entry/1015594?section=official-list-entry