The Picnic at Hanging Rock mansion, Martindale Hall, Clare Valley: Still creepy after all these years

It's 2011 and a visitor to historic Martindale Hall at Mintaro, in South Australia's Clare Valley, is having trouble keeping tabs on her young son who keeps disappearing into a room on the first floor.

Eventually she coaxes him out but he's annoyed at having to leave his friend.

"What friend?" And here is where the story - conveniently printed out and placed on a mantelpiece in the room in question - sends a shiver up visitor spines.

The boy insists he's been playing with a girl with long curly hair who "looks like an angel". No such child is found. But a boy with long hair - as was the fashion - did spend an inordinate amount of time in that room more than 116 years ago. Valentine Mortlock, one of the six children of grazier and politician William Tennant Mortlock and his wife, Rosye Tennant, is said to have suffered some sort of illness or disability. While he was much loved, his life seems a sad one. He apparently ventured out of his room so little that even some of the Hall's live-in maids did not know he existed. As proof, visitors are shown grooves in the floor at the doorway to his room – remnants of a gate used to keep poor Valentine, who died at just eight years of age, inside.

The tale of the apparent ghostly reappearance of Valentine, so-called because he was born on Valentine's Day, is just one of many stories that lure visitors from the area's vineyards, about two hours' north of Adelaide, to this intriguing Georgian-style 1879 mansion, recognised by many as the set for the school that housed those ill-fated girls in the 1975 Australian film classic Picnic at Hanging Rock.

First there is the sheer scale of the 32-room mansion that sits plonked on the South Australian landscape like a lost and puzzled member of the English aristocracy. In its heyday Martindale Hall boasted a polo ground, stables, a cricket pitch (where the English XI were said to have once played), a racecourse, servants' quarters for 14 staff, and that other aristocratic must-have – a boating lake.

Valentine's father bought the Hall and its grounds in 1891 from the man who built it, wealthy pastoralist Edmund Bowman Jnr, heir to Martindale Station. He was forced to sell his prized creation partly due to drought and a collapse in wool prices, but mainly because he over-extended himself in a frenzied pursuit to replicate the lifestyles he saw around him when he was a student in Cambridge. Armed with a big inheritance and even bigger ambitions, Bowman hired 60 tradesman, many of whom were brought out from England, to spend almost a year building his home out of local sandstone, complete with seven-room cellar, and decorating it with carved marble fireplaces (scrubbed with cow dung to keep them sparkling) a special boudoir for visiting mistresses, and exquisite furnishings, including an enormous billiard table he imported from England that can still be seen in the library. It was so big that it was put in situ before a wall was added.

Valentine's brother, Jack, born in 1894, inherited Martindale Hall when his parents died, after being the only one left standing following the deaths of his five brothers and sisters. He travelled widely and visitors to Martindale Hall can enjoy the fruits of his wanderings: rare ceramics, tribal masks, photographs, stuffed animals, wallpapers, paintings and even a suit or armour, or lose themselves in the hedge maze outside.