NO-one forgets their first Beltane Fire Festival.

Mine came in impromptu fashion in 1997 when, as a 19-year-old student, my curiosity was piqued by crowds of oddly attired people drifting towards Edinburgh's Calton Hill, while in the distance came a throbbing drum beat.

Up on the hill, in the shadow of the majestic pillars of the National Monument, a beguiling story was unfolding. I'll be the first to admit that I didn't have a clue what was going on, only that it was magnificent.

The heady smell of bonfire smoke lingered in the crisp air, every so often a flash of colour coming from within the darkness as a crowd several hundred strong, with little more than a thin layer of body paint to stave off the evening chill, swayed to the mesmerising sound of drums.

It was all too much for one interloper who was last seen hotfooting it from the hill, having declared that a "mass orgy" was about to take place. Thankfully, a veteran of the event was on hand to explain the origins of Beltane, once he had finished guffawing: it's derived from a Gaelic Celtic word meaning "bright/sacred fire", and the festival is held to celebrate the blossoming of summer.

Agog, I watched entranced as the May Queen was ambushed by the Red Men, before the Green Man was ritually killed and stripped of his winter guise to be resurrected in that of spring.

Afterwards, I held hands with a school dinner lady and a 74-year-old retired veterinarian to dance rambunctiously around the glowing bonfire. I stumbled home in the early hours and later that day made my way to the polling station to vote in my first General Election, convinced this was the coolest 24 hours anyone had ever spent.

This year marks the 25th anniversary of the event which takes its roots from the ancient pagan festival of Beltane – or Bealltainn – marking the end of winter and arrival of summer, a celebration of the fertility of the land and animals.

At its heart is the sacred Neid Fire, the source from which bonfires were lit and the animals within a community then driven between in the belief that the smoke and flames would purify the herd, protecting them for the year to come.

People in turn would light torches from the fire to ignite their own hearths.

Through the generations Beltane died off, but was given new life in 1988 by co-founder Angus Farquhar, of the industrial music group Test Dept, now head of the arts organisation, NVA. Touring Europe, he was inspired by the open-air festivals in countries such as Spain, Italy and Poland. Another strong influence was the Burning of the Clavie, an annual ritual which takes place in the village of Burghead on the Moray Firth.

"I discovered that Beltane was once a bigger festival than Hogmanay," he says. "It was the key festival in the Celtic calendar. There was real power in these festivals and a strong sense of community as well as something beyond the day-to-day existence, what some people would define as magic. My idea of magic is an intensification of what it is to be alive, the idea that you could create these moments that become windows to something beyond our normal daily existence.

"Beltane used to take place on Arthur's Seat for hundreds of years before it was stopped by the Kirk in the late 19th century. It seemed appropriate, as an Edinburgh boy, to reinitiate the festival, but with a contemporary take on it."

From its humble beginnings as a word-of-mouth event with only 20 performers and a 200-strong audience, Beltane has grown into a major festival which attracts more than 12,000 revellers.

"I'm probably the only person who has seen all 25," muses Farquhar. "In the beginning, we saw things through to dawn. There were always a few complaints about the noise, but it was an amazing atmosphere. We did a lot of fire-running, clearing a rough route through the fire and running through it.

"In the early years I was always uproariously drunk and drumming for six or seven hours. There have been occasions when the drumming has gone on for hours, with 100 or 200 people all inside the rhythm with that sense of freedom, of being lost within the fire and the power of the drum."

Chair of the Beltane Fire Society, Matthew Richardson, became involved as a student 14 years ago. "I was blown away by it," he recalls. "It was unlike anything I had ever seen before. I enjoyed the spectacle, although that first night I didn't exactly know what was going on."

Richardson has undertaken various roles including a fire performer, drummer and a White Woman in the May Queen's court. Most recently he has been a Blue Man, one of the old hands of Beltane who maintain its rituals, traditions and history.

The Blue Men act as mentors to those new to the event and as guides of the procession and protectors of the May Queen.

Described by Farquhar and Richardson as an "honour" and "incredible role", the May Queen can't nominate herself. She must be chosen by the elders of Beltane. There have been five over the past 25 years, the most recent, Erin Chadwick, holding the title since 2010.

"The May Queen has a humility," says Farquhar. "She carries and embodies the whole presence of Beltane through a channelling of the energy on the night. It's an incredibly dignified, beautiful, powerful and quiet position. All the women who have had the role over the years have manifested it brilliantly."

Chadwick, 29, a chef, originally from Victoria, Australia, admits to initially being overawed by the prospect. "I have spent the past three years wondering why I was chosen," she admits. "I never asked or expected to be May Queen, they [the organisers] just showed up at my door one day and told me this was now my role. I had to get used to the idea very quickly."

She laughs when asked if the role brings May Queen groupies. "For some people you do represent a goddess or some spiritual figure, for others it is the life and cycle of nature. To be everything to everyone, and allow them to project what they need on to you for that night, is a powerful thing. To be that symbol is an honour."

Such is the intensity of Beltane that Chadwick, like all the festival performers, gets lost in the ritual. "Beltane is something you have to see to understand," she says. "Until you have felt the energy and seen the grandeur first hand, you don't really get it. My parents will be here for Beltane – it will be their first time. Bless their hearts, they are going to get a bit of a shock."