The drone of the man’s oak didgeridoo reverberated off the granite. “Not that I know when Doomsday is,” he said, parting his lips from the mouthpiece and pointing toward the 19ft tall thick, grey stones a few yards from us. “But whenever it hits, this is right where I’d want to be.”

I met Anthony, a hitchhiker from North Carolina, at the site of the Georgia Guidestones, a mysterious six-piece granite monument atop a desolate hill in the small town of Elberton, Georgia. He had stopped at the site on his way to see the Coral Castle – another mysterious stone structure – in Homestead, Florida. I had stopped because I’m a sucker for roadside oddities.

“It's no wonder this was chosen as the site for the guidestones. Elberton isn't called the 'Granite Capital of the World' for nothing,” Anthony said. "Right now we're on a deposit 35 miles long, six miles wide and three miles deep. If there was ever going to be an earthquake or natural disaster, I'd want to be right here atop six million tons of solid stone. This would be where society would survive.”

It was this gargantuan granite deposit that attracted a well-dressed man under the pseudonym of RC Christian to Elberton in June 1979. He approached the Elberton Granite Finishing Corporation’s President Joe H Fendley Sr about the potential cost of building a monument of substantial size, explaining that he represented a small group of anonymous Americans foreign to Georgia who had been working on a 20-year-long project as a message for future generations. Fendley promptly put him in touch with his banker, Wyatt C Martin, who was soon chosen as the intermediary for the project. Both men were sworn to secrecy.

On 22 March 1980, the Georgia Guidestones – four giant rough-edged stones encircling a centre slab with a capstone balancing on top – weighing 119 tons, were revealed to a crowd of about 100 people. One crowd member, a local pastor, immediately professed his belief that the stones were built for cult and devil worship because of its similar appearance to Stonehenge. On each side of the capstone, engraved in four ancient languages, were the words: “Let these be guidestones to an Age of Reason.” And written in eight languages – English, Russian, Mandarin Chinese, Arabic, Classical Hebrew, Swahili, Hindi and Spanish – were cryptic instructions for rebuilding society post Doomsday:

“Maintain humanity under 500,000,000 in perpetual balance with nature; Guide reproduction wisely – improving fitness and diversity; Unite humanity with a living new language; Rule passion – faith – tradition – and all things with tempered reason; Protect people and nations with fair laws and just courts; Let all nations rule internally resolving external disputes in a world court; Avoid petty laws and useless officials; Balance personal rights with social duties; Prize truth – beauty – love – seeking harmony with the infinite; Be not a cancer on the Earth – Leave room for nature – Leave room for nature.”

After his encounters with Fendley and Martin, Christian left town and was never seen again. All he left was an explanatory stone tablet a few yards from the monument, detailing the astrological placement of the stones: the four main granite slabs were aligned with the celestial poles, while the centre stone was drilled with an eye-level hole oriented with the North Star and a slit aligned with the Sun’s solstices and equinoxes. The capstone, having its own slit, was to act as a calendar, revealing the date at noon each day when the sun shone through.

It’s clear that extensive thought went into the building and placement of the guidestones. But the reason for its existence and the true meaning behind the stones’ messages have never been confirmed, nor understood.

“As far as maintaining the population, what happens if you’re the one person over 500,000,000?” laughed a woman in her late 60s (who asked not to be named) as she rang up my Styrofoam cup of Cajun-boiled peanuts at a gas station down the road from the guidestones. A silver bun was gathered on top of her head, stray hairs catching in the clasp of her American flag necklace, and her voice dripped with Southern charm in between sips from a lipstick-stained Diet Coke can.

“We have people from all over who come for the guidestones,” she said. “A lot of people come for the vibes – some think it’s good, some think it’s eerie. Some just don’t know what to think.”

She adjusted the gold chain of her necklace. “For me, the first time I saw them, I thought they were creepy. I’ll just say it reminded me of Stonehenge. And everyone knows what went on at Stonehenge.” Her pale cheeks tinted by a rose blush dropped solemnly.

I bit into a boiled peanut. “What’s that?”

“Human sacrifices, of course.”

Although there’s never been any confirmed link to the occult or sacrificial rituals, she told me of a case in March 2015, when a hobbyist drone picked up footage of what was thought to be blood smeared on top of the capstone.

“Most locals around here don’t really think one thing or another about them, but there have been some local pastors who say there’s cult-y stuff going on. I think the sheriff's department dismissed the case, but if someone really did perform a ritual, I wouldn’t be all that surprised. We’ve had people come in and deface it, write “ISIS” all over it. We even just had a lady get married up there, and she was a witch.” Her face perked back up. “But a good witch.”

Thousands of people each year come to visit the guidestones. And among the sceptics, supporters, conspirators and those simply passing through, there exist a number of theories on the identity of Christian and the true nature of the stones.

Some people, such as Yoko Ono, praise the guidestones as a call to rational thinking, while others think they’re the words of the Antichrist. Some even believe the monument's dimensions predicted the height of the Burj Khalifa 30 years before the iconic Dubai building was even constructed. But Anthony, like many others, believes that Christian is part of the Rosicrucian Order, a community that studies the metaphysical laws of the universe, and thinks that Christian has been granted the elixir of life.

“I think R C stands for Rosy Cross, which is the emblem of the Rosicrucian Order,” he said. “Their whole goal is complete transcendence between the astral, mental and physical planes and to know the essence of all three of those states of being. For that, you'll need lifetime after lifetime after lifetime of knowledge. I believe Christian is one of the Ascended Masters who has this knowledge that he’s passing to us through these stones.”

“You think he's still around?” I asked.

He put the didgeridoo back to his lips. “Of course. But as far as who or where he is, I don't think we'll ever know.” The didgeridoo droned. “But as to whether these guidestones are going to help us all after the end of the world, I guess we’ll have to wait and see when Doomsday hits – whenever that may be.”