Sanctum: Making the 3-D Cave Diving Adventure (Yes, a Gigantic Fish Tank Was Involved)
Photograph courtesy Universal Pictures
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Alister Grierson, director of the new adventure film Sanctum, had never donned flippers and an oxygen tank before he signed on to join 3-D pioneers James Cameron and Andrew Wight's underwater thriller about a cave diving expedition gone wrong. The premise (which Wight describes in this interview): The world’s largest cave system is being mapped by divers when a tropical storm dislodges rocks that block the entrance. The team, which includes two tagalongs who are not experienced cave divers, is forced to find another way out, if they can survive. This study of human behavior under pressure is something that fascinates Greierson, who made his first film Kokoda about a WWII invasion in Australia, to great box office success. Here Grierson gives a fresh take on the submersive, high stakes world of cave diving and how they replicated it for the film (yes, a 130-foot fish tank was involved).—Mary Anne Potts
ADVENTURE: What did you know about cave diving before this movie came along?
Alister Grierson: Very little. It’s one of those sports you hear about, but usually you only when someone dies in a cave. Then you say to yourself, why the hell were they down there?
Tell us about going diving for the first time?
It was before pre-production had begun. We all agreed I needed to get into a cave to have the experience and translate that for the film. But I wasn’t a diver at all, so I had to learn to scuba dive. I did a two-day intense course with John Galvin, who wrote the screenplay. He’s a master diver and he taught all the actors to drive. On day three they put me in the cave in a place called Mount Gambier in South Australia.
It must have been shocking to go from learning to dive one day to dropping into a cave the next?
I have always been adventurous and keen to try new things. So I was willing. I was very confident that it would be safe, that they wouldn’t push me to do anything too risky. I mean cave diving is inherently risky, but I knew I had a good team to look after me. I picked up on the diving pretty quickly.
Take us through your first dive, as if we were actually there.
Every cave is different. The South Australian cave system is very unique; the area is dairy farming land. It’s like Swiss cheese under there. Cows are often found having fallen through.
There’s a big hole, like a man hole, that goes through the Earth like 20 meters. And you get out and you prepare and you put your wetsuit on. Experienced cave divers wear drysuits because it’s so cold. First you lower all your diving gear down through the well and into the water. They set up an A-frame and they lower you down into the manhole. That’s the most confronting bit. Then you break through then it’s like an underground lake, about the size of an Olympic swimming pool. It was big, very big. The roof of the cave is a couple meters above the water level.
Then you enter the water?
You get into the water, and it’s freezing cold and pitch black. So you turn your lights and go under. The first thing that hits you is the clarity of the water—it’s crystal clear. And that’s really quite stunning. It’s really a surreal environment. It’s pitch black and only your lights are guiding you. It’s kind of like you are diving a river. You are negotiating estuaries and tubes and trying to get a sense of the ancient space.
And it’s beautiful. And as Andrew Wight describes, you get a sense of flying. There’s no noise. When diving in the ocean, there’s not the ambient crackle sound. In a cave, the sound of your own breathing becomes hypnotic.
I was struggling just to learn how to dive, let alone really enjoying the moment. But I think I understand why these guys are driven to do this. It’s really interesting and different. The guys who really go hardcore, like the expedition leader in our film, want a great personal challenge.
So everything went smoothly on your first cave dive?
Well, I did have one panicked moment. We’d been gone for two days on our expedition. I was tired so I volunteered to be the first person to get out of the cave. The last thing we had to negotiate was this body tube, which was like 80 feet long. So I am squirming, worming through this thing, and suddenly I hit this wall of rock. There’s only one way out of here, and I think, Oh no, there’s been a cave collapse! Then I was really starting to panic. I thought, We’re screwed! But what happened is that there was this ledge and I went under it instead of over it. And so just for that brief moment I was totally in this headspace of being in a collapsed cave. So I kind of get it.
You experienced the basic premise of the movie—the terror of having the entrance blocked.
Yes. I’m not sure if I am ever going to be a cave diver. I like the idea of doing more diving, and looking at reefs, though.
As much as this film is about extreme adventure, there seems to be something universal in these relationships? I like doing stories about real people in real scenarios. Obviously this was a fictional event, but it examines people under pressure and how they respond. In these disaster-style movies, you try to find a hyper-realized version of life. You are sort of telescoping the life experience into 12 hours, or whatever it is, and so it becomes almost operatic in scope. Some people respond well in those crisis moments. Other people don’t.
Watching the characters evolve is fascinating, you practically forget about the whole 3-D aspect.
That’s our strategy and Jim’s [James Cameron’s] philosophy. First of all, it’s got to be a comfortable experience for the audience. Secondly, it’s about immersing them in the world of 3-D and getting hooked into the story. And the cave environment works really well for that.
Can you tell us about shooting on location compared to shooting in the 131-foot tank?
What we realized really quickly is shooting on location in caves is really hard. Obviously there are safety issues, but the logistics are really hard. Like water temperature, for example. Even in a drysuit, the longest you can stay in the water is really 90 minutes. So if you are lucky, you could shoot two blocks of 90 minutes a day to do it. And that’s just too restrictive on finishing a film.
- Nat Geo Expeditions
So you built a set?
We rebuilt the cave in the tank, flooded it, built ceilings over, then shot it at night to replicate the feeling of complete darkness. And then we could heat the water, which is the biggest asset. We had people in the water for 12 hours a day.
We had to keep the water clean. That’s the other thing about caves, they silt up really quickly. You’ve just got millenia of dust that settles on everything. So as soon as you move it, it makes the visibility zero. So we would bring in our own silt so that we could filter it out and clean it as we needed to, depending on the shot.
And most important it was safe. We taught all our actors to dive using rebreathers. So for all intents and purposes they were cave diving. It was that much safer. We could control the environment that much better. We had safety divers always at an arm’s length.
These actors had pick up a lot of new skills. Diving, yes, but rappelling, rock climbing, BASE jumping?
They all went for it. When they read the script, then would have known that it would have a lot of work. They love learning that stuff, but also it’s a way into their character, it’s something they could grab on to. With Alice [Parkinson, who plays Victoria], she loved all the climbing stuff and the abseiling stuff it was a way for her to understand what her character was all about
But Rhys [Wakefield, who plays 17-year-old Josh] did all the hard work. He did the climbing, ropes, the leaping, and the underwater stuff. The final thing he does in the movie, with breathing the bubbles along the ceiling of the cave. He did that himself. He did a lot of training to do it. I tried it, too, and I gave up. It’s really quite serious because as soon as you go into it, your head fills with water, it goes right up your nose. It fills your ears, it’s really disorienting. Then you have to move along the surface of the roof. And you really have to breath that air. He was really impressive.