Pre-booking advised. The Shell Grotto is one of the world’s most mysterious places: a series of underground rooms and passageways covered by 2000sqft of exquisite mosaic created with 4.6 million shells. Discovered in 1835, nobody knows who created it, when, or why. “The grotto is simultaneously haunting and homely. It could be a lost pagan shrine or have ‘A Present From Margate’ picked out in the shells - it wouldn’t matter. It’s still magical, mysterious and (once it’s in your head) impossible to forget.” Far From the Sodding Crowd: More Uncommonly British Days Out, Penguin Books.