The Shell Grotto is a complex of underground rooms and corridors covered in a 2000sqft mosaic built with 4.6 million shells, making it one of the world’s most mysterious places. Nobody knows who made it, when, or why it was discovered in 1835. “The grotto is both frightening and welcoming. It doesn’t matter if it’s a long-lost pagan shrine or if the shells have the words “A Present From Margate” written on them. It’s still wonderful, intriguing, and tough to forget once it’s in your head.” Penguin Books, Far From the Sodding Crowd: More Uncommonly British Days Out.