The collection, Anya-Petrivna explains, was started by the author’s grandmother. “Back in the 19th century, everyone gave Valentine’s Day cards,” she explains.

“We now associate it with romantic love, but back then, it was love and affection [more generally].”

The celebration had a kind of gravitational pull in Lindsay’s life: when she was young, the family would gather around the album to admire the anonymously given cards and their brightly coloured, sometimes scented envelopes.

As an adult, Lindsay wrote the cards into Picnic at Hanging Rock – and fans of Peter Weir’s 1975 adaptation of the work will be able to see several that were featured in the film.

Though the originals are too “precious and delicate” to be handled, the National Trust has painstakingly digitised the cards and made reproductions at scale, allowing for a closer encounter with the objects.

Alongside the album, visitors to Mulberry Hill will be able to view tantalising ephemera from Lindsay’s life: scrapbooks made during her school days; an anniversary card illustrated by her husband; mementos from the film; and a poem given to Lindsay on St Valentine’s Day “from someone mysterious”, according to Anya-Petrivna. “We haven’t been able to work out from who.”

A collection of typewriters are assembled in the dining room, which visitors to the house are welcome to use to write their own poems or anonymous notes.

For the most part, Anya-Petrivna has approached the space with a light touch: “The house is an as-found experience,” she explains. “It’s very much as if Joan has just left for a moment. We just want to really evoke that spirit of place, that idea that Joan was there.”

The house has been maintained almost exactly as Lindsay left it – as though inside its four walls, time has stopped.

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Throughout her career, Lindsay was repeatedly asked to explain Picnic at Hanging Rock – to clarify whether it was based on a true story, to answer all those unanswered questions. The excised final chapter of the book, published after Lindsay’s death, only serves to raise more questions – about time, about patterns and repetition, about the nature of Hanging Rock itself.

For Anya-Petrivna, this is typical of Lindsay’s life more broadly: “She had this really otherworldly quality about her.

“She merged interest in things like physics and maths, with a kind of mystical quality – she did believe in another dimension, in something that was kind of quite esoteric; in this life force, in this idea of coincidence and synchronicity.”

But Lindsay never defined her beliefs, either publicly or in any of her papers. For her, they were deeply personal and private.

As curator, Anya-Petrivna has the privilege of being able to handle Lindsay’s personal effects – to flick through the album and touch the St Valentine’s Day cards. But, she notes, Lindsay pasted many of the cards down.

Opening them – and reading the messages inside – has been rendered impossible. Whatever mysteries are held between their pages are destined to remain just that.

My Day of Days is on at Mulberry Hill, Langwarrin South, each Sunday starting from February 11 to March 31.

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