There are conflicting accounts of the grotto’s discovery, although most agree on a date of 1835. The earliest reference to the discovery appears in an article in a predecessor of the Kentish Mercury of 9 May 1838:[1]

Belle Vue cottage, a detached residence, has been lately been purchased by a gentleman, who, having occasion for some alterations, directed the workmen to excavate some few feet, during which operation the work was impeded a large stone, the gentleman being immediately called to the spot, directed a minute examination, which led to the discovery of an extensive grotto, completely studded with shells in curious devices, most elaborately worked up, extending an immense distance in serpentine walks, alcoves, and lanes, the whole forming one of the most curious and interesting sights that can possibly conceived, and must have been executed by torch light. We understand the proprietor intends shortly to open the whole for exhibition, at small charge for admission.

It has remained in private ownership ever since.

In 1932, the then new owner took over the grotto, and soon afterwards substituted electric lighting for the gas lighting that, over the decades, had blackened the once-colourful shells. Cleaning trials show that in the majority of the grotto, the shells have lost their colour under the dirt and are white.[2] The structure has also suffered the effects of water penetration, though was removed from the Heritage at Risk Register in 2012 after a five-year conservation programme, carried out in partnership with English Heritage. A scheme to sponsor replacement mosaic panels – The Roundel Project – was established in 2012.

The Friends of the Shell Grotto was formed in 2008 and is a not-for-profit trust established to promote, conserve, and preserve the grotto as a unique historical monument.