Following his Spielberg-esque animation Monster House, director Gil Kenan has returned with the new fantasy City of Ember. Based on the book by Jeanne Duprau, the movie tells the story of two teenagers, Doon and Lina, who live in the underground city of Ember that is slowly beginning to die. He speaks to David Grove about the making of the Steampunk adventure.

How did you get involved with City of Ember?

It happened right after I got out of film school. I’d made a thesis film called Lark that got me a lot of attention in Hollywood, and all of a sudden I found myself out of school and taking meetings in Hollywood. This is before I developed Monster House.

One of my first meetings was with Tom Hanks’s company, Playtone, and I remember that I sat down with them and I just started pitching them all of these crazy ideas, lots of science fiction stuff. I was so nervous. Then they showed me the manuscript for City of Ember, which hadn’t yet been published, and they asked me to read it and then come back and give them my take for the movie.

What did you think when you read Jeanne DuPrau’s book?

I read the whole thing that night, and it was one of those things where I immediately saw the movie in my head, saw the world in the story, as I was reading it. I went back to Playtone and laid out my vision for a three-hour movie and they really liked it, and we went from there. I really loved the book. I loved the idea of making a city, a city as amazing as the one in our film, a character in the story. As it turns out, I think the movie I saw in my head when I first read the manuscript is very close to the finished film.

What was it about the city in the story that intrigued you so much?

The city is a great character all by itself, really the main character in the story. I loved the metaphor and symbolism of a magical city that’s kept alive by this pulsing generator that serves as the city’s heartbeat. Then the generator becomes sick, the heart starts to fail, and the city is dying. What are the citizens going to do? That’s what the story’s about. It’s about a city with a beating heart, a city that’s also populated by interesting and colourful characters.

What was the biggest challenge in adapting the book to the screen?

Visualizing the city was something I did as I was reading the book so that actually wasn’t very difficult for me. The hardest part was creating the design of the city itself, showing the complex and interwoven puzzle that explains how the city runs, how the heart beats. The descriptions in the book are often very brief, maybe one or two sentences, whereas in the movie they’re big visual moments, huge set-pieces.

Another challenge, in terms of storytelling, is that the book is really about puzzle solving, children figuring out things in their heads, and how do you translate that to a visual medium? I had to create a film that was also like a puzzle where you have these children, who are teenagers in this film, who have to solve puzzles and decipher clues in order to find their way out of the city.

In the book, Doon and Lina were 12 and in the movie they’re teenagers. Why did you make them older?

We looked all over the world for actors and then I met Harry Treadway, who plays Doon, and he was so amazing that I just had to cast him even though he’s older. When I met Saoirse Ronan, who’s amazing, I knew we had to make the characters older in the film. They were the two best young actors I could find so I had no choice, and I also think it serves the story better because the dynamic between two teenagers is more interesting and different than two kids. Harry and Saoirse were so great that their ages became irrelevant.

How would you describe the visual style of the film?

The book is set far in the future, and the city looks like it’s been built on top of our world so you see in the film how Earth as we know it today has become an ancient relic. City of Ember is set in the Steampunk era and it has that look and vibe. The city is full of these old contraptions that have been brought back to life for the modern age and tweaked and reconstructed. An example is how Lina plays a pedal-driven phonograph to put her sister to sleep at night. There’s pedals and pulleys everywhere.

The city is dying and there’s lots of visual clues of that in the film, especially with the old generator itself. The generator is buried beneath the city and it’s a ten-storey structure that really is the city’s heartbeat, and it’s dying and that causes everything in the city to slowly degrade. It’s like a human with a weak heart.

How involved was Tom Hanks?

Tom had the manuscript and developed the project and he really loved the story. We worked closely together when I was working on the screenplay and he was my biggest supporter in terms of me getting the job. He visited the set in Belfast and was very supportive. He loved walking around the sets. He was amazed by them.

How difficult was the transition from the animated world of Monster House to making a big budget live-action film like City of Ember?

It’s night and day. On a film like Monster House you’re in total control of what the scenes look like and where the camera moves. On a film like City of Ember we would sometimes have to go through walls and rearrange sets just so I could get a single shot I wanted. In animation you have 100% control of your scenes, of the frame, and you don’t have that on a live-action film so it’s been quite a learning experience.

Working with actors is a whole other story. On Monster House, I basically made that film in post-production and created the performances during the production of that film. With City of Ember, I had to talk to the actors every day.

Does City of Ember have a lot of practical effects?

Yes, very much so. That’s why we went to Belfast because we wanted to build sets in a realistic setting. I wanted to build a city, and I knew I couldn’t do that with visual effects because it wouldn’t look right, especially with the actors. I didn’t want this to be a green-screen movie; I wanted to build a city.

We built Ember in the same place they constructed the RMS Titanic. The building we worked in is 100 feet tall and we also worked in whole apartment buildings. It’s an enormous set, which it has to be when you’re building an underground city. We worked in the Harland and Wolff paint hall in the Titanic Quarter in Belfast where the Titanic was painted after being constructed in the nearby shipyard, so it’s quite a historic place. We actually built a village in this place, complete with apartments and little stores so you really feel like you’re in Ember. On Monster House, I would point at a spot and say, “Okay, there’s a monster over there or a haunted house there”, but on City of Ember the city was there for us.

What was it like working with Bill Murray, who plays Mayor Cole in the film?

Bill’s a great guy. You hear stories about how eccentric he can be but he’s great to be around on the set and he makes everyone else feel good, especially the other actors. Caroline Thompson wrote the script and Bill’s a big fan of her collaborations with Tim Burton and that’s what attracted him to this project. He liked the script and his character and we met on the golf course and he agreed to do the film.

Bill’s our villain in the film and he’s a politician - a gorging, fat politician - so that makes him even more of a villain, but what’s great about Bill is that he’s a villain you love to hate. He wears a fat-pad in the film and he looks really funny. That’s Bill. Even when he’s being bad you love him.

City of Ember is released in US and UK cinemas on 10 October 2008.