'Avatar,' the Deep Dive, an exclusive first look at the making of 'The Way of Water'

When "Avatar" first premiered in theaters during the holiday season of 2009, and eventually became the highest-grossing film of all time, the world and entertainment space were on a different planet.

Moviegoers barely had streaming choices, big-name franchises like the Marvel Cinematic Universe were in their infancy and smartphones were slowly making their way into consumers' hands.

Director James Cameron told ABC News that he knew making a follow-up 13 years later that moved the story forward and satisfied fans around the world wasn't going to be easy, but it was a challenge that he was up for.

"Do I want to invite lightning to come and strike the same place again? Of course, my final answer was go big or go home," he said of "Avatar: The Way of Water," which premieres Dec. 16.

ABC News got an exclusive behind-the-scenes look at the making of the sequel in an hour-long special "Avatar: The Deep Dive," which airs on Dec. 13 at 10 p.m. ET and streams the next day on Hulu, and spoke with Cameron, the stars and the crew about the new depths they reached to create the film.

The film will be distributed by 20th Century Studios, which is a division of Disney, ABC’s parent company.

The original movie ended with Earth soldier Jake Sully rejecting his superiors at a mining corporation and joining the alien Na'vi in their fight against the humans who tried to ruin their environment and displace them for the rare mineral "unobtainium." Sully permanently kept his mind in his Na'vi avatar to be with his love interest Neytiri.

Cameron said "Avatar: The Way of Water" picks up the characters' love story 15 years later and their new challenges from humans and other tribes on Pandora.

"I think there's a conscience of the first film which I wanted to continue, which is around our remaining natural spaces and how civilization is encroaching on them," he said.

Sam Worthington and Zoe Saldaña, who played Sully and Neytiri respectively, reprise their roles and said they had no problem getting back into their motion capture suits to portray their 10-foot blue alien characters.

"I can find different ways to describe a James Cameron experience but grueling is definitely not in the first five," Saldaña said. "It's passionate, it's fun, it's inclusive, because [of] what he is creating."

"I've always said 'I'm his soldier.' Jim's this director I'll do anything for, but he's in the trench right there next to me," Worthington said.

The protagonists are joined by a whole host of new Na'vi characters. The crew looked at thousands of actors to play the young characters such as Neteyam, Lo'ak and Tuk, Sully and Neytiri’s sons and daughter.

Baily Bass, who plays Tsireya, the daughter of Ronal and Tonowari, who are played by Kate Winslet and Cliff Curtis respectively, said getting the role was a life changer.

"We didn't have much, but we always got through it because my mom's just the best," Bass said of her family. "And then I'm sitting in my mom's car and I start tearing up because…I reached this moment in my life, in my career, where I can take care of my family."

Not all of the young characters were played by newcomers. In fact, through cutting-edge visual effects, Cameron was able to give one of the first film's stars new life as a new character.

Sigourney Weaver played Dr. Grace Augustine in the first film, a character who is killed by the humans, and in "The Way of Water" she portrays Kiri, Jake and Neytiri's adopted teenage daughter.

Weaver shared how Cameron explained he wanted her to play someone who was 14 years old.

"He said, 'Come on. We both know you're 14 at heart. So I don't think this is going to be a problem for you,'" she said.

Weaver said she worked with Cameron to fine-tune Kiri's characteristics, taking note from her own adolescence.

"Jim gave me total freedom, and I just would let Kiri out," she said.

The visual effects team was able to take Weaver's performance and seamlessly make her appear as a teen, but she said she still had to go through the same training as her younger co-stars.

Cameron's vision and passion for deep ocean diving meant that the cast had to dive deeper to achieve his vision for the story, which sees the lead characters taken in by a Na'vi water clan.

Most of the sequel will take place underwater and in the ocean and the director was insistent that his actors were filmed and motion captured deep in real water.

"When you're underwater, it's easy to pretend to be the character and just stay in the scene and be like, OK, now I'm in the oceans and interacting with this creature," Jack Champion, who plays "Spider," said.

The entire cast had to learn intense free diving techniques so they could perform underwater for long periods.

Kirk Krack, a lifelong free diver who can hold his breath underwater for up to 7 minutes, began training the cast on his techniques back in 2017. The cast would be submerged 30 feet in water tanks and learn to extend the time they can hold their breath.

By the end of the training cast members said they were able to hold their breath for long periods. Some, like Winslet, were able to hold their breath for close to 7 minutes.

"You do go into this meditative almost trance-like state because you have to relax," Winslet said. "You’ve got no option because you use more oxygen holding that breathe than you do thinking about other things."

The cast and crew said they are proud of the feats they accomplished to make this film and a third movie, which was filmed simultaneously and scheduled to release in 2024.

They said they are confident the film will impress longtime "Avatar" fans and bring in new ones as well.

"If I'm going to go down this rabbit hole, let's see how deep we can go with it, metaphorically and physically," Cameron said.