Bellevue-based game developer Bungie opened its doors to fans Monday to celebrate its first post-Microsoft title, Destiny, which launched at midnight.

Notoriously secretive, given the fandom surrounding its popular Halo series, Bungie’s downtown headquarters was inundated with fans as early as Saturday, camping out in line for a chance to see its inner workings.

“I’m surprised we’re being so open,” said Derek Carroll, senior designer for Destiny, Bungie’s mythical sci-fi first-person shooter. “Our fans are what make us, besides our crazy drive.”

Fans lined up around Bungie’s headquarters on 106th Avenue Northeast, and were ushered in groups through the company’s two floors, first getting a glimpse of its workstations. They were later brought downstairs, where game developers signed Destiny merchandise, before fans engaged in Destiny’s competitive gameplay.

“It was really cool to see the line forming,” said Eric Osborne, head of community at Bungie. This was the first time the game developer had opened its doors to the public since relocating to its Bellevue headquarters in 2010. Osborne said it won’t become standard practice. “This is really just to celebrate Day One (for Destiny).”

Destiny had already launched in Australia first, and was just about to go live in Europe when Bungie’s doors opened.

The title was hailed by Gamestop as the largest new game preorder of all time, said Genevieve Waldman, spokeswoman for Activision, which is under a 10-year partnership with Bungie to produce four Destiny games. Two expansion packs have already been announced.

“This game is alive,” she said. “There’s going to be something new to do in this game every single day. It’s a living, breathing organism, quite frankly.”

Development for Destiny started small, as Bungie was completing Halo Reach, and was led primarily by the company’s co-founder, Jason Jones, said Carroll. In 2010, the focus of Bungie’s 500 Bellevue employees switched gears to Destiny. Unlike its Microsoft-exclusive Halo games, Destiny is available on four platforms: PS3, PS4, Xbox 360 and Xbox One.

“It’s a whole new engine for the future,” Carroll said. “It really plays great on all four platforms it’s released on.”