It started out as an idyllic vacation for a mother, a father and their three young sons on the West coast of Thailand. But the winter holiday soon turned to a living hell -- and an epic fight for survival -- when the young family got caught up in the most devastating natural disaster in modern history.
It was Dec. 26, 2004, when a giant Indian Ocean tsunami swept across Southeast Asia, destroying entire villages and five-star resorts, and killing hundreds of thousands of people.
"The Impossible," which will be in theaters nationwide on Dec. 21, tells the true story, in excruciating detail, of what happened to the Belons, a family who was caught up with millions of people in the disaster.
Naomi Watts plays the mother, Maria, alongside Ewan McGregor, who plays her husband, Henry.
"It just felt like it was rooted in real truth," Watts said. "Every line of dialogue, every detail, everything just felt real, and I had to do it. I knew I wanted to do it from five pages in."
In the film, Maria and her son Lucas barely survive the initial wave. Maria is badly injured and Lucas is convinced the rest of their family didn't make it. Facing unimaginable obstacles, the mother has to rely on her son to help her and other survivors.
"She was sure that she was going to die," Watts said of her character. "So it was absolutely vital to her to impart this need to take care of others. That was something that was really, really important to her."
The real family is from Spain. Lucas Belon is now 18 years old. Maria Belon was deeply involved in the production of the movie and even spent months on set in Thailand. Watts said she and Belon spent hours talking to each other in her preparation for the role.
"I wanted to get into her mind of every moment that took place in these 48 hours," Watts said. "She would just let it pour out of her."
The 2004 tsunami killed more than 200,000 people and left millions homeless. To capture the horror of the event, director Juan Antonio Bayona did not rely solely on computer-generated special effects. Instead, his team built a huge tank filled with rushing water and debris.
"We were truly in an uncomfortable situation, which was a massive water tank, being thrust one way, water coming this way, water coming behind you, side pumps, debris, garbage, everything thrown at you," Watts said.
"The Impossible" is Bayona's English-language debut. In Thailand, they filmed in the exact hotel, now rebuilt, where the Belons were staying when the tsunami hit. Real survivors were used as movie extras and Watts said she heard many talk about their experiences.
"Every day was a new story," she said. "We were around it every single day, whether you were on the set, or back at the hotel, there were always reminders of it, because everybody was connected to it in some way."
Watts has very few speaking lines in the film -- she only has two pages worth -- and conveys all of the emotion of her character using hardly any words. In one scene, local Thai women help Maria get dressed, which Watts said was very touching.
"Those Thai ladies who were dressing me after losing my clothes and everything, and taking care of me, and that was just incredibly moving," she said.
The actress has never shied away from tough, dramatic roles, from "21 Grams" to "The Ring Eastern Promises," but she wasn't always in demand.