Shell Grotto, Margate
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.
The Shell Grotto consists of a winding subterranean passageway, about 2.4 metres high and 21 metres in length, terminating in a rectangular room, referred to as The Altar Chamber and measuring approximately 5 x 6 metres.
The excavations are entirely underground. Steps at the upper end lead into a passage about 1.07 metres wide, roughly hewn out of the chalk, which winds down in serpentine fashion until it reaches an arch, the walls and roof of which here onward are covered in with shell mosaic. The arch leads to what is known as the Rotunda, a central circular column, meeting at the farther side at the Dome - a shaft rising to the surface, capped to allow some daylight into the structure. The plan of the sub-base of the Dome is triangular, equilateral, and with an arch in the centre of each side. The two arches in the sides are those leading from the Rotunda, whilst the arch in the base leads into the Serpentine Passage. This passage, with its curving walls, and over-arching vaults is rich in mosaics of varied design. At the end of the Serpentine Passage, a further arch leads into the Rectangular Chamber. Here the decoration takes on a more formal and geometric character, but still finely drawn and executed. The subjects are chiefly star and sun shapes. The focal point, the "altar" is the arcuate niche which faces the entrance arch.
Attached to the grotto is a museum, gift shop, and cafe.
The purpose of the structure is unknown, and various hypotheses have dated its construction to any time in the past 3,000 years. Hypotheses include: it was an 18th or 19th-century rich man’s folly; it was a prehistoric astronomical calendar; it is connected with the Knights Templar/Freemasonry. No scientific dating of the site has been done.
The most frequently used shells throughout the mosaic – mussels, cockles, whelks, limpets, scallops and oysters – are largely local. They could have been found in sufficient numbers from four possible bays: Walpole Bay in Cliftonville; Pegwell Bay especially at Shellness Point, Cliffsend, near Richborough; Sandwich Bay, Sandwich; and Shellness on the Isle of Sheppey. The majority of the mosaic is formed from the flat winkle, which is used to create the background infill between the designs. However, this shell is found only rarely locally, so would have been collected from shores west of Southampton, where it is abundant. 
There are conflicting accounts of the Grotto’s discovery, although most agree on a date of 1835. The earliest reference to the discovery appears in an article in the Kentish Gazette of 22 May 1838, announcing its forthcoming opening as a public attraction. 
It has remained in private ownership ever since.
In 1932, the then new owner took over the Grotto, and soon afterwards substituted electric lighting for the gas lighting that, over the decades, had blackened the once-colourful shells. Cleaning trials show that in the majority of the Grotto the shells have lost their colour under the dirt, and are white.  The structure has also suffered the effects of water penetration, though was removed from the Buildings at Risk Register in 2012 after a five-year conservation programme, carried out in partnership with English Heritage. A scheme to sponsor replacement mosaic panels – The Roundel Project – was established in 2012.
The Friends of the Shell Grotto were formed in 2008 and are a not-for-profit trust established to promote, conserve and preserve the Grotto as a unique historical monument.
- Algernon Robertson Goddard THE GROTTO OF GROTTOS - A DESCRIPTIVE LEAFLET July, 1910
- Algernon Robertson Goddard THE ROMANCE OF THE GROTTO - A DESCRIPTIVE LEAFLET September, 1903
- Shell Grotto Archive
- Shell Grotto Archive
- Shell Grotto Archive
- Nigel Barker, Allan Brodie, Nick Dermott, Lucy Jessop, Gary Winter - Margate’s Seaside Heritage (Informed Conservation), published by English Heritage, 2007 (ISBN 978-1905624669)
- Harold Bayley - The Lost Language of Symbolism, published by Ernest Benn Ltd, 1974 (ISBN 0-510-40801-X)
- Howard Bridgewater - The Grotto, Rydal Press, Keighley, Yorkshire, 1948, and Kent Archaeological Society, 3rd Edition, 1957
- Dorothea Chaplin - Matter, Myth and Spirit, published by Rider & Co, 1935 (ISBN B0000D5LFU)
- Harper Cory - The Goddess at Margate, printed by Henry Burt & Son Ltd, Bedford, 1949
- Lionel and Patricia Fanthorpe - The World’s Most Mysterious Places, published by Hounslow Press, 1999 (ISBN 0-888-822-065)
- Ruby Haslam - The Shell Temple, published by Regency Press, 1974
- Ruby Haslam - Underground Mythology – Edited by Sylvia Beamon, Chapter 1, The Shell Grotto at Margate, published by Able Publishing, 2002 (ISBN 978-1-903607-20-6)
- Ruby Haslam - Reality and Imagery: The Grottoes of Margate and Twickenham, published by Athena Press, 2009 (ISBN 978-1-84748-349-2)
- Michael Howard - Earth Mysteries, published by Robert Hale, 1989 (ISBN 0-709-039-336)
- Hazelle Jackson - Shell Houses and Grottoes, published by Shire Publications, 2001 (ISBN 0-7478-0522-9)
- Barbara Jones - Follies and Grottoes, published by Constable, 1953 (ISBN B0000CINFP) and revised second edition, 1974.
- Rod LeGear - Underground Thanet, published by the Trust for Thanet Archaeology, 2012
- Patricia Jane Marsh - The Enigma of the Margate Shell Grotto, published by Martyrs Field Publications, 2011 (ISBN 978-0-9569437-0-5) and revised second edition, 2014.
- C. A. Mitchell - The Grotto - A Study of One of the First Great Civilizations, Cooper The Printer Ltd, Margate, c.1949
- Sonia Overall - The Realm of Shells, (Novel), published by Fourth Estate, 2006 (ISBN 0-00-718410-7)
- Nigel Pennick - The Subterranean Kingdom, published by Turnstone, 1981 (ISBN 0-855-001-402)
- Conan & Nellie I. Shaw, The Shell Temple of Margate - An Archaic Masterpiece, printed by Cooper The Printer, Margate, 1954
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