The sun was shining on a cool, calm April afternoon as Aldie Mackay settled into the passenger seat for the drive along the picturesque north-western shore of Loch Ness.

The journey along the A82 into Inverness was one the manageress of the Drumnadrochit Hotel had made many times with her husband, John.

This time, though, as their little car trundled along the lochside road close to Abriachan pier, something odd caught her eye.

“Stop!,” cried Aldie, eyes trained on the bubbling waters of the loch. “The beast!”

As John brought the couple’s car to a shuddering halt on that April day in 1933, the floodgates opened - and have never really closed.

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For Aldie’s claim that she’d seen an enormous creature with a body resembling that of whale thrashing in the dark, cold water kickstarted a lingering mystery which, 90 years later and despite expeditions, scientific tests, sonar surveys, grainy photographs – some less convincing than others – the deployment of a yellow submarine and, in 2013, the bizarre appearance of Hollywood’s Charlie Sheen on a monster hunt with leg of lamb for bait, remains as perplexing and fascinating as ever.

From the moment her startling news emerged, the search for the elusive and enigmatic Loch Ness Monster was on.

A few days after her sighting 90 years ago, on 15 April, 1933, Aldie stood in the bar of the hotel she managed and happened to mention what she’d seen to Loch Ness water bailiff Alex Campbell, a part-time journalist.

His Inverness Courier story, under the headline “Strange Spectacle in Loch Ness”, was packed with thrilling detail, the kind that would attract Nessie-hunters in their masses for years to come.

"The creature disported itself, rolling and plunging for fully a minute, its body resembling that of a whale, and the water cascading and churning like a simmering cauldron,” he wrote.

The Herald: Cruise Loch Ness

“Soon, however, it disappeared in a boiling mass of foam.

“Here was no ordinary denizen of the depths, because, apart from its enormous size, the beast, in taking the final plunge, sent out waves that were big enough to have been caused by a passing steamer.”

Back at Drumnadrochit, Aldie’s hotel bookings jumped as curious tourists descended.

While reports of monster sightings and the odd grainy photograph – including one captured in November that year by Hugh Gray of Foyers which, unlike some others, has never been disproved - came thick and fast.

Today at the modern Drumnadrochit Hotel -  alongside Aldie's former hotel which is now the Loch Ness Visitor Centre - guests still arrive hoping they might be the ones to solve the mystery.  

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And if not, there’s always the hotel’s Nessie Shop packed with the next best thing: dozens of emerald green fluffy Nessies with ‘googly’ eyes, tartan bunnets and bow ties.

“We’re all things monster here, even our WiFi password is Monster!,” concedes Donald Macleod, the general manager and Nessie believer.

“Business is great, we’re full for Easter and it’s looking like it’ll be a busy season.

“The chat among the guests tends to be about how they’re looking for the monster. They’re definitely still coming for Nessie - and they’re still looking.”

He does it too: “Any time I’m walking or driving by the loch I’ll have a wee look,” he adds, “you’re always hoping that something catches your eye.

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Pictured: Impressions of the new Loch Ness visitor centre

“Of course, I’m a believer - I’m a good Scottish lad and Nessie is part of our national story.

“Plus, you can’t see all these ripples in the loch, hear all these rumours and stories and not believe there’s something there.

“And until we find it, no-one really knows.”

Although her sighting kicked off a modern phenomenon, Aldie was far from the first to report mysterious creatures lurking in water that plunges to more than 880ft deep: tales of beasts have swirled around Loch Ness since the Middle Ages, linked to Saint Adomnán’s 7th century account of Saint Columba banishing a “water beast” in the River Ness.

But her account came at a time when movie goers were gripped by monster movies like King Kong, and  mysteries like Big Foot, the Bermuda Triangle and UFOs grabbed newspaper headlines and gripped the public.

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Soon there would be many more Nessie sightings -  bank managers, students, lorry drivers, fishermen, lawyers and clergymen all claimed to have seen the monster.

And they still come thick and fast. This week dad of three John Payne, 55, a visitor from Newport in Wales, spotted a strange movement in the water while admiring the Loch Ness view from his guest house Foyers Roost in Inverness.

The image he captured appears to show a mystery object with “a huge neck”.

While last month, Nessie hunter Eoin O'Faodhagain, 58, said he had spotted a 30-feet long shape, and two humps breaching the surface of the loch.

Willie Cameron’s father Ian was a police officer and later detective superintendent, adding authority to his  June 1965 account of a strange object travelling through the water.

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“He was with three or four other people,” Willie recalls. “They watched an object for 15 minutes travelling with the wind from Urquhart Castle, then turning against the wind.”

The sighting was corroborated by tourists on the shore, who also witnessed the strange scene.

“It had a mind source and power source: it went against the water and rotated in the water not because it was being driven by the wind, it went back because it wanted to,” he adds.

Willie went on to work in tourism – some might say a sector that more than benefitted from a mysterious creature popping up at the start of the holiday season.

Known as ‘Mr Loch Ness’, his role as Highlands’ ambassador and founding director of Cobbs Group, a thriving bakery and hospitality business based in Drumnadrochit, has taken him all over the world. 

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Wherever he goes, he says, everyone wants to discuss Nessie.

“It’s one of the world’s greatest mysteries. Loch Ness is as famous as any ocean in the world.

“It is one of the hooks that brings people to Scotland and as far as tourism is concerned, it’s one of the jewels in our crown.”

He points out that Loch Ness attracts around 1.5m visitors every year – 360,000 to Urquhart Castle – helping to boost the local economy by up to £50m.

But while there is beautiful scenery, invigorating walks, cycle trails and sports events, Nessie, he says, is the star attraction.

The Herald: Cage for Loch Ness monster

Pictured: Hunters have tried to capture Nessie in a variety of ways, including this purpose-built cage

“It’s possibly looked on slightly negatively by some who ridicule Nessie as a down market product, but any tourism business CEO would be happy to have a Loch Ness Monster.

“The Loch Ness Monster is hotter now on a global basis, than in the whole 90 years since Aldie Mackay’s sighting.”

Mike Bell, owner and captain of Loch Ness Cruises – with its Nessie Hunter boat fitted with colour sonars that scan the loch floor – agrees: “I’d say 90% of the tourists who come to Drumnadrochit want to look for the monster.

“There are all these wonderful Highland views, beautiful walks, cycle trails and it’s almost as if no-one gives a toss. It’s all about the monster."

Does he believe? "The more time I spend on the loch the more possible it seems that there is something living there,” he says.

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“It’s entirely possible that there is something there that we haven’t discovered yet and perhaps won’t for many years.”

Now in its 90th year – give or take 1,500 years – Nessie’s story is boosted by social media mystery hunters and YouTube, which loves a good, unsolved tale to hook in viewers.

While soon Nessie hunters will soon have a new focal point, when the revamped £1.5million Loch Ness Centre opens in the former Drumnadrochit Hotel where Aldie once worked. 

It promises to take visitors through 500 million years of Loch Ness history, using immersive technology borrowed from some of the UK's biggest attractions, including The Real Mary King's Close and  Coronation Street: The Tour in Manchester. 

With The Official Loch Ness Sightings Register claiming 1,145 sightings to date and theories spanning everything from giant eels to prehistoric plesiosaurs, will the mystery ever be solved? 

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Willie believes the truth is out there.

“Even if 90% of sightings are explained – a bit of wood, deer swimming, otters or floating timber – there’s still a lot that aren’t,” he says.

“It is a vast area of loch, 24 miles long, 2 miles wide. We are just mere mortals, who are we to say there’s nothing there?

“It doesn’t make one iota of difference if it is solved, and people say there’s nothing there – there’ll still be lots of people who will disagree and say there is.

“Whatever happens we are in a win-win situation.”