In 1835, a man named James Newlove and his young son, Joshua, stumbled upon a secret cave whilst digging a pond in Margate, Kent. Well, so the story goes.

This cave was covered in a giant mosaic, made up of 4.6 million seashells. No one knows how long the shells have been there, who put them there or why.

There are many theories surrounding the origin of the adorned cave, now known at the Shell Grotto, including its possible use as a meeting place for a secret sect, a religious shrine and a rich man’s folly. The truth is no one knows. Nearly everything about the cave is shrouded in mystery; even the story of its discovery is dubious.

What they do know is that 99% of the shells are of British origin, although there are also Caribbean shells in the Altar (the rectangular chamber at the back of the cave).

The Grotto is Grade I listed and protected by English Heritage, yet sadly it has been on the at risk register since the 1990s due to dampness. The shells are very dirty due to the gas lamps that were used to light the cave in the past, meaning they almost look like part of the walls. Cleaning the shells isn’t viable as it would potentially cause damage.

Being in the Grotto was quite surreal. I felt like I was in some kind of tomb and began to wonder just what else was under the ground. There’s not a lot to explore (70ft of underground passages) but you’ll be mesmerised by the sheer volume of shells, and probably spend some time, as I did, picking out symbols and patterns such as flowers and stars.

The above images show displays of shell art available to view before you descend into the cave, including a sailor’s valentine from the late 19th century (far right), brought home from Barbados by a sailor for a loved one.

Entry to the Shell Grotto is £3.50 for an adult. Open daily from 10am to 5pm