Hidden beneath an ordinary residential street in the seaside town of Margate, England; is a place that seems to have been built by a mermaid.
A narrow staircase leads down through the chalk into a series of underground passages, where almost every visible surface is covered in seashells. Millions of them, arranged into intricate patterns that climb the walls, curve across vaulted ceilings and disappear into the shadows; resembling a forgotten temple, or an elaborate tomb. And perhaps the most unsettling thing about it – is that nobody knows for certain who created it, when it was built, or what it was originally intended to be.

The grotto was brought to public attention in the 1830s, after its discovery beneath what was then private property. By 1838, it had opened as a visitor attraction, yet its origins were already a mystery. No surviving records definitively identify its builders or explain the purpose of its elaborate decoration. Over the years, theories have ranged from an ancient religious sanctuary to a wealthy landowner’s ornamental folly. Some have suggested connections to pagan rituals, while others believe it was constructed during the late Georgian or early Victorian period. Despite generations of speculation, the grotto has never yielded a universally accepted explanation for its existence. It simply feels like the remains of an elaborate project whose creators have been erased from its history.

Approximately 4.6 million shells cover around 2,000 square feet of walls and ceilings. The layout also adds a sense of mystery – with narrow passages winding through the chalk, opening into a domed chamber before continuing towards a rectangular room traditionally known as the Altar Chamber. There is little natural light and almost no visual connection to the town above. The ordinary world seems to disappear as soon as you descend the staircase. It truly is a real life Backrooms in the most maximalist, fairytale sense.

Photo credits: “Shell Grotto, Margate (12)” by american_rugbier, CC BY-SA 2.0 , “Shell Grotto 4” by Barney Moss, CC BY 2.0 , “Shell grotto walls” by Alastair Campbell, CC BY-SA 2.0 , “day in Margate” by Peter Blundell, CC BY 2.0 , “DSC_7373” by Andrew H, CC BY 2.0