'Pacific Rim's' Charlie Hunnam Says Filming Was Like Running on Worst Elliptical Ever (Video)

The cast of Guillermo del Toro's tentpole also talks to THR about their first reaction to seeing the massive monsters and robots on the big screen.

When the cast was preparing to shoot Pacific Rim, director Guillermo del Toro made sure to show them plenty of sketches to explain what the giant monsters and robots would look like in the end product.

But the actors reveal that no amount of explanation from their fearless leader could have prepared them for what came alive onscreen.

PHOTOS: Giant Robots vs. Giant Monsters: 6 New 'Pacific Rim' Posters

"Nothing really prepared us for the actual end product. When you see the film, you're like, 'Wow, these bastards are big!' " Idris Elba tells The Hollywood Reporter.

The Warner Bros. and Legendary film, which stars Charlie Hunnam, Elba, Ron Perlman, Charlie Day and Rinko Kikuchi, is set in a future when the human race in threatened by giant monsters called Kaiju that rise out of the sea. They build massive robots (called Jaegers), which require two pilots connected mentally thought a neural bridge, to battle the creatures.

"I think there's more personality and humanity in these inanimate objects than has ever been seen before," Perlman tells THR. "The Jaegers are all like jocks. Some of them are real hot-dog show offs, some of them are down to the nitty gritty, and some of them are like martial artists. Every one has a personality."

Hunnam, who stars as one of the Jaeger pilots, agreed with his Sons of Anarchy co-star.

FILM REVIEW: Pacific Rim

"Not just the monsters and the robots -- just the whole world that Guillermo created, I thought was just so detailed and textured. I think he did a beautiful job creating this rich world that was completely original," says Hunnam.

One thing that del Toro created for Pacific Rim was an actual pilot chamber which the actors would film in when they were navigating the robots. Hunnam says the physical challenges of those scenes were more difficult than he expected.

"[My co-stars] had all been in there beforehand, and so I had heard all of the horror stories, and I thought, 'God, you know, these Hollywood actors, let me show you how a real man is going to handle this situation,' " he says. "And then I got in and I realized I had grossly underestimated the demand of this thing."

"It's like being on an elliptical machine for 14 hours a day, on hardest resistance, wearing a suit of armor that weighs 40 pounds," he adds.

Watch THR's interview with the cast above to find out whose mind they would like to delve into through a neural bridge.

Pacific Rim opens in theaters Friday.

E-mail: Rebecca.Ford@THR.com
Twitter: @Beccamford