Who are these indomitable-looking ladies in fur? And what are they up to? Looks to me like they might be channeling messages from the other side. There’s ectoplasm in the air.

They are in fact having a seance, in one of the strangest, most mysterious places I’ve visited in a while. The picture was taken in Margate’s Shell Grotto in the 1930s. The grotto itself is open to visitors, and it’s brilliant. You descend down a tunnel cut into the chalk under a Margate back street, and into a series of chambers and tunnels covered in 4 million shells. The story of the grotto is that it was discovered, fully-formed, in 1835. A man digging a duck pond lowered his son into a hole in the ground that had opened up (health & safety!), who reported back that he’d seen a cave covered in shells.

The grotto – unlike the handful of Georgian-era grottos in the country – is not set in a country estate, but built under what was farm land. And despite the work it must have taken to create, no one in the town had any memory or record of it being built. Theories range from a pagan temple to a meeting place for a weird cult. Quickly after its discovery the owner of the land opened it to the public, lit by gas light. It is very atmospheric today but by flickering, smoky light it must have been incredible.

All but a few of the shells are found locally – humble whelks, mussels, cockles and some oyster shells hauled up from various beaches in their thousands and laid into intricate patterns that are wonderfully open to interpretation. It’s still privately owned, and can be hired – it’s been a location for TV and also some interiors shoots. I’ll be booking it for my 40th birthday seance next year.