It was no surprise to MacGillivray Freeman's film crew that the cave in Little Colorado River Canyon had never been explored. Not only were there no roads to this location, the cave was on a cliff 300 feet below a plateau and more than 700 feet above the river. The 'easiest' way into the cave was from the plateau above. Helicopters flew the 30-person crew and 3-1/2 tons of gear to and from the site each day.

A team of expert riggers devised a 20-foot truss and winch that lowered crew and equipment down the sheer cliff to the cave entrance. MFF trusted this venture to rigger and production manager Earl Wiggins whose last job was overseeing the safety of Tom Cruise in Mission Impossible 2. Director of Photography Brad Ohlund was impressed with the result: "Not only did Earl and Mark Chapman build a system for getting people and gear into an impossible location, they created shooting platforms in no time flat. I just had to show them where I wanted the lens, and literally, only minutes later, the camera and tripod would be rigged solid." He continued, "They quickly understood that in IMAX®, we always need to put the camera where it doesn't want to go."

"There were certainly major technical challenges shooting IMAX® footage in the vertical ice shafts of Greenland, but nothing of any technical nature even approached the sheer magnitude of sitting on three thousand feet of ice, or realizing at the bottom of one of the ice caves that we were not even a fifth of the way to bedrock, " said Cinematographer Gordon Brown.

The most difficult shots were deep within Minnik, the near 600-foot ice cave. The crew needed to set up a platform close to the bottom of the cave to film the characters' descent. At this depth, the ice is under 300 pounds of pressure per square inch, making the ice walls very unpredictable. On one ascent, when a crew member merely kicked the ice wall with his crampons to get a hold, a 100-foot crack rifled across the face of the walls above them. Though the film and caving team tried their best to purge the icy shaft of icicles, they realized even the smallest of loose shards could prove dangerous, even deadly, if they plummeted hundreds of feet to the crew below.

The falling ice caused the crew to abandon the filming platform and move to a 9600 pound ice block, wedged precariously in the shaft, but just around the corner from the platform and out of the way of falling ice. As the film team used ice screws to secure their position, they heard another sharp snap as the block beneath them shifted a quarter-inch. They watched a crack move in slow motion up the wall for about 40 feet. The block shifted another quarter inch. Continues Brown, "The disturbing part was that the ice block did not settle or roll, but continued to grind away at its trappings a quarter inch at a time. Every five minutes our hearts stopped as we felt our footing shudder and we heard an awful snap and grind. There wasn't anything to do but keep shooting."

The foremost question was: how do you light an environment that's in total darkness for a film format that needs four to ten times the intensity of lighting that conventional filmmaking needs? The large format film frame is ten times larger than 35mm film, so more light is necessary to expose each frame properly. In Hidden Worlds, the production crew used HMI lights, concentrated, white lights powered by generators at the surface.

Even more challenging was figuring out how to light a scene that looked natural and that followed cavers moving through an underwater environment as if their hand-held lights were the only source. Underwater Director of Photography Wes Skiles said: "If you do it right, no one will ever notice the lighting in the film. If you do it wrong, everyone will notice."

The crew used fifteen hundred feet of cable that branched out to five different light heads at varying depths in the cave. In order to light giant rooms as divers flew through them on underwater vehicles, Skiles cued underwater grips stationed at each light source to flag or cover the light in a choreographed pattern as the film's characters moved through the scene. Adds Skiles, "The biggest challenge was timing. Our incredible underwater grip and electric team had the method down to a science, and many of the most difficult lighting scenarios ever attempted were captured beautifully on the first take."

The topside crew, led by the film's Director of Photography Brad Ohlund, faced their own lighting challenges. The primary "dry" cave location was actually flooded with one to four feet of water, making the use of lights very precarious. Ohlund adds, "Lighting these caves requires creating enough depth and texture to show off the dramatic formations without it seeming to be lit artificially. The audience needs to feel they are part of the adventure, not watching a movie."