If you've felt a recent urge to unleash your inner Viking, you're not alone: millions of people have been riding the waves, swigging mead and slaying the enemy in a craze for the video game "Valheim".

Designed by a tiny Swedish games studio, "Valheim" has proved an unexpected smash-hit, selling five million copies since its early-access release last month on the online gaming platform Steam.

At one point, more than half a million people were playing online simultaneously.

"We didn't expect this kind of success at all," said Henrik Tornqvist, co-founder of Iron Gate, the company behind it.

"We are overwhelmed, humbled, and under a lot of pressure."

The five-strong team that developed the survival game have not yet been able to meet up to celebrate due to the pandemic, Tornqvist said.

"Valheim" players can learn to hunt, make armour, build Viking longhouses and eventually slay terrifying monsters as they explore the vast and fantastical world.

"It's quite a refreshing game and a really great one, whether you're talking about the light, the backdrop or the music," said 25-year-old player Pierre Galissant, who has already spent 60 hours roaming its plains, forests and swamps with three comrades.

'Valheim'; the latest hit video game set in the vital and violent world of the Vikings
'Valheim'; the latest hit video game set in the vital and violent world of the Vikings AFP / Kilian FICHOU

Tornqvist suspects the ability to team up with friends is part of the game's appeal.

"Our game being co-op focused is part of our success for sure," he said. "And also the Viking theme."

"Valheim", which is still in development, is just the latest hit video game set in the vital and violent world of medieval Scandinavian warriors.

Norse mythology has inspired game designers for decades, from late-90s series Baldur's Gate to strategy games like Age of Empires II.

But Jean-Christophe Piot, a writer and host of a podcast about mythology, said there had been "a real revival" around the seafaring Vikings, who raided, traded, and settled around Europe between the 9th and 11th centuries.

Norse influences are hardly new in pop culture, he pointed out -- Marvel Comics introduced Thor, god of Thunder, as a character in 1962.

"But they've appeared in video games on an unprecedented scale in recent years," he said.

Clive Standen, Katheryn Winnick and Gustaf Skarsgard, stars of the 'Vikings' which has fostered interest in the world of Scandinavian warriors
Clive Standen, Katheryn Winnick and Gustaf Skarsgard, stars of the 'Vikings' which has fostered interest in the world of Scandinavian warriors GETTY IMAGES NORTH AMERICA / Alberto E. Rodriguez

Iron Gate consciously chose this setting for "Valheim" because of the existing Norse craze, Tornqvist said, citing the 2013 TV series "Vikings" as a contributing factor.

The latest instalment of the wildly popular game franchise "Assassin's Creed", released in November, plays out in several different historical periods -- but it too takes players on a Viking adventure.

"Fans had been demanding it for ages," said Thierry Noel, a historian who worked with French studio Ubisoft on the development of "Assassin's Creed: Valhalla".

Far from sticking to stereotypes of bloodthirsty barbarians in horned helmets, Ubisoft wanted to avoid cliches and introduce a degree of historical rigour, said Noel.

"The idea was to try to identify grey zones -- parts of history where you can slip in without affecting the historical version of events as we know it," he said.

"In the case of the Vikings, it was relatively easy. We don't know that much about this period, they left few traces," he explained.

"That leaves a bit of space for creativity and imagination."

It's a bet that paid off: "Valhalla", set in 9th-century England, is the franchise's biggest hit yet.

Sony also jumped on the Norse bandwagon in 2018 for the latest part of its "God of War" saga, which previously focused on the Greek gods.

After selling more than 10 million copies in a year, the eagerly awaited follow-up "Ragnarok" -- the Norse apocalypse -- is due later this year.

"I think 'Valheim', absolutely, to some degree lives on the success of those other games," said Tornqvist, who also cites "The Legend of Zelda: Breath of the Wild" and "Skyrim" as sources of inspiration.

For some, the Viking game's constantly-evolving universe also offers an antidote to the pandemic at a time when very few of us are travelling.

There are five different zones to explore and the developers say there will be nine by the official release date, which is yet to be announced.

"There's an escapism to it, which works well at the moment," said Galissant, adding that the game had allowed him to go on some very pleasant "walks" in the Scandinavian forest.

Noel agreed. "We want adventures, wide open spaces, discovery," he said.

"We are living in a time where we want to be Vikings."