The group, tourists from Britain, Germany, the US and half a dozen other countries, followed the guide deep into Tollymore Forest and gathered around a tree stump.

“Ladies and gentlemen, cameras ready,” said Eric Nolan, who had chaperoned them from Dublin to this state park in Northern Ireland this week. “This,” he said pointing, “is where Kit Harington’s arse sat.”

Nolan grinned and held a poster-sized screenshot showing Harington, the actor who plays Jon Snow, indeed sitting on the stump in an early episode of Game of Thrones.

The visitors clustered around the stump and aimed their cameras. Click, click, click. It was probably the least dramatic moment of the day-long tour – there would be a castle, replica weapons and petting wolf-like dogs – and still they were enchanted.

Such is the spell cast by the HBO fantasy saga, which returns to screens on 14 April for the eighth and final season, a television phenomenon with 30 million devotees in the US and millions of others in the UK, where it is broadcast on Sky Atlantic.

The tale of rival kingdoms, battles, bonking and dragons in Westeros has won 47 Emmys thanks to blockbuster budgets, stellar talent and source material in the form George RR Martin’s bestselling novels.

The show has also created a tourism boon for Northern Ireland, which hosts most of the filming, drawing tens of thousands of fans to sets and locations and £30m in spending each year, according to Tourism Ireland.

The agency has negotiated a licence agreement with HBO recognising Northern Ireland as official Game of Thrones territory, facilitating multiple spin-offs and a certain irony: a tourism industry stunted by the Troubles now benefiting from fictional mayhem.

Grace Kurosaka, left, and Victoria Niblett, friends from Alabama, in Tollymore Forest. Photograph: Rory Carroll/The Guardian

More than 150,000 people have viewed an 80-metre long tapestry depicting scenes from the show, including coronations, beheadings and stabbings, at the Ulster Museum. It will be displayed later this year alongside the medieval Bayeux Tapestry in Normandy.

“One thing that makes Game of Thrones so popular is its worlds are so recognisable,” said Victoria Niblett, 24, a student and dancer from Alabama who toured Tollymore Forest dressed as Daenerys, the dragon-whispering heir of the Targaryen dynasty. “Here you can immerse yourself; it’s a coexistence of reality and fantasy.”

Some of her companions donned woolen cloaks resembling those worn by the Stark family, a procession which prompted one startled dog-walker to wonder if they were part of a Celtic ritual.

“One thing I can tell you about the mega-fans is that they’re mental,” said Nolan, 30, an ebullient Dubliner. When not leading bus-loads around Northern Ireland he works as an extra on the show playing a primitive Wildling, which contractually necessitates a long beard and long hair.

Ryan Fahey, a US air force pilot, dons a cloak during a Game of Thrones tour. Photograph: Rory Carroll/The Guardian

During tours some fans go on bended knee and propose to partners, he said. One couple spoke fluent High Valyrian, a fictional language invented by Martin, having learned it from an app. “They come from everywhere: Alaska, you name it.”

But after the final episode airs on 19 May and viewers presumably learn the fates of Cersei Lannister, Sansa Stark, Lady Brienne and other characters, and discover whether zombie White Walkers seize the Iron Throne, will interest ebb and visitor numbers dwindle? To paraphrase Jon Snow, is winter coming for Game of Thrones tourism?

Rob Dowling, the managing director of Game of Thrones Tours, which runs 30 coaches a week from Belfast and Dublin, is not worried. “Look at the other things happening,” he said. HBO is due to start filming a prequel spinoff series this year, which could hook devotees for another decade. The TV network is also preparing to turn four locations and sets into visitor attractions, promising a “scale and scope bigger than anything the public has ever seen”.

The tourists in Tollymore Forest did not doubt Game of Thrones would thrive beyond the screen just like Harry Potter and Lord of the Rings attractions.

“It’s because of the characters. You have your favourites and the ones you hate,” said Nikki Basquine, visiting with her mother from England.

A tourist on the Game of Thrones trail in Tollymore Forest. Photograph: Rory Carroll/The Guardian

Ryan Fahey, an air force pilot from Arizona, noted the peril of having favourites. “You start rooting for people and then they die.”

There have been 174,373 deaths in the show so far, according to one estimate.

Jeff Carbaugh, 56, was confident the popularity would endure. He and his bride Lara, 53, flew 7,000 miles from their home in Hawaii to honeymoon in real life Westeros. “I introduced her to Game of Thrones. If she liked it she was a keeper,” he joked.

Nolan declined to divulge information about the upcoming season. HBO would come looking – “I’d be shot” – and as a mega-fan himself he does not want to give spoilers.

As the tour bus headed to its next destination he shared tidbits about gruelling battle sequences – “25 days kicking the shit out of each other for your entertainment” – and Kit Harington’s allure. “He’s proper good looking. I’m not gay. He just is.”