Shell Grotto in Kent

Discovered in 1835 in Kent, England, the Shell Grotto (Grotto Hill, Margate, Kent, CT9 2BU, U.K.; phone 08143 220008) is a 70-foot-long subterranean passageway whose walls and ceiling are covered with mosaics made of seashells, at least 4.6 million of them. When was it created? By whom? And why? It remains a mystery.

Five minutes’ walk from Margate’s seafront (20 minutes from Margate Station), the grotto is open 10-5 daily from Good Friday to Halloween and 11-4 weekends only from Nov. 1 to Palm Sunday. Closed Dec. 25 & Jan. 1. £3 (near $5) adult, £2.50 senior or student, £8 family.