Florian Zeller, still basking in the glow of 'Bunker's' rapturous reception at the Venice Film Festival, reflected on the powerful connection with the audience. 'It’s a powerful moment because you never know how something is going to be received,' Zeller explained via Zoom. Drawing from his theater background, he noted, 'When it works, when emotions are shared and what you’re trying to give, is received, it’s very powerful.'

Zeller believes the thunderous applause was not just for the taut thriller he crafted, but equally for the compelling central performances by Penélope Cruz and Javier Bardem. The couple portrays a husband and wife whose relationship faces an ultimate test when the husband considers building a doomsday bunker for a tech billionaire. The genesis of this unique premise struck Zeller after reading about Meta founder Mark Zuckerberg's own elaborate apocalyptic compound in Hawaii.

“I was fascinated by this paradox, that this man who built his fortune on the idea of connecting people, was working on a plan B at the same time to isolate himself from the rest of the world,” Zeller stated. He realized this paradox extends beyond physical bunkers, describing an 'internal or more invisible bunker, where you can almost believe that you don’t need the rest of the world. Where everything can be delivered directly to you, like food, of course, but also cinema, friendship, social interaction, love, sex. The world outside is not a place you really have to explore anymore.'

Seeking the perfect on-screen couple to inhabit the modernist townhouse where much of 'Bunker' unfolds, Zeller immediately thought of Cruz and Bardem. His reference point was Stanley Kubrick’s 1999 erotic drama, 'Eyes Wide Shut,' which famously cast then-married Tom Cruise and Nicole Kidman as a couple navigating marital strife. Zeller recalled the 'strange sensation' 'Eyes Wide Shut' evoked, blurring the lines between truth and fiction due to the real-life couple's involvement, creating an 'exciting insecurity as a viewer.'

However, when Zeller pitched Bardem on recreating an 'Eyes Wide Shut'-esque dynamic with his wife, the actor was quick to caution him. “Javier told me, ‘You should not really mention this film in front of Penélope anymore,'” Zeller recounted. Bardem’s reasoning was poignant: 'Because remember at the end of that shooting, Tom and Nicole got separated.' Zeller understood the inherent risk of a real-life married couple delving into the complexities of a fictional marriage in crisis.

However, Zeller emphasized that 'Bunker' diverges significantly from Kubrick’s film, focusing not on the fissure of a marriage, but its restoration. 'That was where we were going, and it allowed them to go very far into emotional places because they knew that all of this energy was dedicated to the idea of reconnecting to each other in the end,' he explained.

This distinct perspective is even subtly woven into a visual reference. Zeller re-stages a moment from 'Eyes Wide Shut' where Kidman’s character’s dress falls to the ground, revealing her bare back. In 'Bunker,' however, Cruz is seen putting on her gown. 'It’s the reverse,' Zeller noted. 'That’s because the film is about reconciliation. That’s the destination. That’s the journey.'

Filming for 'Bunker,' though set in London, took place on a soundstage in Madrid, conveniently close to Cruz and Bardem’s home. Zeller elaborated on this practical decision: 'They are a father and a mother, and it happens to be very important for them to be good parents and to take care of their children. And when one of them is working, the other one has to take care of the family. So there was a real practical question about what to do with the children, and I thought because the film is about reconsidering the priorities of your life, it was important for them to be close to the people they love.'

Despite the intense psychological battles their characters endure, Zeller observed that Cruz and Bardem had no trouble delivering emotionally charged scenes. 'They were really interested in catching the reality and the truth of the scenes, and they were helping each other get there,' Zeller said. 'During the takes, they knew what to say to each other to trigger the anxiety or the anger or the energy that we were looking for. They have been together for so long, that they obviously used that.'

'Bunker' marks Zeller’s third feature film, following his Oscar-winning 'The Father' (2020) and 'The Son' (2022). Known for his emotionally resonant plays, Zeller is currently directing a stage production but remains deeply committed to cinema. 'My heart and my energy are really toward cinema,' he affirmed. 'I’m worried about what the future holds for this industry and this art form. But we have the responsibility to fight for it and for what we believe in with passion and with courage. There’s something extraordinarily rewarding about people coming together to watch a film.' Indeed, even in the streaming era, sometimes leaving your 'bunker' to experience a film collectively is precisely what's needed.

'Bunker' is slated to screen at the 2026 Toronto International Film Festival on September 14, with Sony Pictures Classics handling its theatrical release in the United States.