Beneath an unassuming spot in Margate, England lies the Margate Shell Grotto, a winding underground passageway discovered in 1835.
It was likely built sometime in the late 18th or early 19th century, though the exact date is unknown.
The walls and ceilings are covered in around 4.6 million seashells arranged into detailed mosaics of patterns, symbols and geometric designs. No one knows for certain who built it or exactly why.
It stretches roughly 70 ft (21 m) underground and remains one of the UKโs most unusual architectural mysteries, part folklore, part Victorian curiosity, still without a confirmed origin story.
๐ท Shell Grotto