The Shell Grotto is an ornate subterranean passageway shell grotto in Margate, Kent. Almost all the surface area of the walls and roof is covered in mosaics created entirely of seashells, totalling about 190sq metres of mosaic, or 4.6 million shells. It was discovered in 1835 but its age and purpose remain unknown. The Grotto is a Grade I listed building and is open to the public.