A beautiful mystery
No one seems to know who created the 2,000 year old Shell Grotto in England. There are 2000sqft of underground rooms and passageways decorated with exquisite mosaic made from 4.6 million shells.
Photo courtesy of: No Swan So Fine, CC BY-SA 4.0 https://commons.wikimedia.org/wiki/File:Shell_Grotto,_Margate,_November_2021_11.jpg_