The Shell Grotto is an ornate subterranean passageway shell grotto in Margate, Kent, England. Almost all the surface area of the walls and roof is covered in mosaics created entirely of seashells, totalling about 2,000 square feet (190 m2) of mosaic, or 4.6 million shells. It was claimed to have been "discovered in 1835", but its age and purpose remain unknown. The grotto is a Grade I-listed building and open to the public.