ENGLAND - SHELL GROTTO in Margate Kent is an underground passage entirely lined with shells. The entire complex is hewn out of the native chalk of Kent and extensively decorated. It was “discovered” in 1835. It is estimated that the builders, whoever they were, used about 4.7 million shells to make the complex. The purpose of the structure is unknown, and various hypotheses have dated its construction to any time in the past 3,000 years.