Grade I listed building. Main construction periods 1800 to 1832. The Shell Grotto was discovered in 1835 by a schoolmaster and his sons digging in their back garden. Mystery surrounded its discovery as it was not marked on any maps of the area, and none of the town's residents knew anything about its construction. Opinion is divided as to the origins of the grotto - it has been identified as Phoenician, Roman, Mithraic, as well as an 18th century folly and more recently as a sun temple. The most likely identification is that it is from the early 19th century as traces of a modern brick remain in one of the Gothic shaped arches. The Grotto is made up of about 4.6 million shells, 2000sq ft of mosaic consisting of 28 different types of shells, many of which are foreign. There are a number of motifs and images in the shell patterns inlcuding common Egyptian, Greek and Indian motifs.