It’s a late afternoon in May, and Yahoo Movies is having a “pinch yourself” moment. We’re in Shepperton Studios’ cavernous H Stage, standing on a glass balcony that’s part of the Avengers Tower interior set. Just below us, there’s a main atrium where the glitziest, most star-studded party you could ever dream of is taking place.

Nearly all of the Avengers have assembled here today: Black Widow (Scarlett Johansson) is perched at the bar, talking to Hawkeye (Jeremy Renner). Meanwhile Bruce Banner (Mark Ruffalo) has just greeted Captain America (Chris Evans) with a bear hug, and Thor (Chris Hemsworth) is chatting up some highly decorated military types. And standing away from all the action, surveying the scene, is Tony Stark (Robert Downey Jr.), who’s sipping a martini and chatting with pal Rhodey Rhodes (Don Cheadle).

The set is incredible. It’s Tony Stark’s ego run amok, writ large in stainless steel and polished glass. There’s a grand piano (which Evans gently plays between takes), a drum kit, and a full gym. Works of art line the walls, as do countless shelves of coffee table books. If it weren’t for the quinjet landing platform that’s attached to the room’s side, it’d be easy to mistake it for an immensely swank hotel lobby.

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The Avengers assemble at their posh mansion in a scene from the Age of Ultron trailer.

"It’s wild, isn’t it?" Ruffalo says later, while we’re relaxing in his trailer. "It’s the ultimate bachelor pad-slash-gym-slash-laboratory."

Banner has his own lab in the tower (it’s suitably green), and Ruffalo explains his character has been working closely with his "Science Bro" Stark in the intervening years between the two Avengers films: “Banner has his own space in the Stark empire. He’s working on some biotech stuff. He’s definitely got a lot on his mind, and some big stuff brewing.”

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Mark Ruffalo and Robert Downey Jr. in Age of Ultron.

If you’ve seen the first trailer, you’ll know that Avengers Tower plays a key part in Age of Ultron, as it’s the setting for an early confrontation between our heroes and the film’s titular villain, who crashes the tail-end of the party we’ve just seen on the set.

We point out to Downey and Hemsworth that having a huge Avengers sign on the tower makes it very easy for the bad guys to seek them out. “Yeah, that’s a challenge for us,” explains Hemsworth. “But it’s also a threat to the bad guys as well. This is where we are.”