The first challenge of "K2" that faced the technical crew at Arena Stage was building a mountain. The mountain had to be climbed, it had to look like ice, and there had to be clouds to indicate that the play takes place at 27,000 feet. And the mountain had to be safe, of course.

But that was just the beginning. Costumer Noel Borden had to make the mountain climbing gear the two performers wore look like down, but not be of down because the actors would get too hot. She made parkas stuffed with balls of nylon net and fiberfill.

The action of the play takes place on a ledge of K2, which at 28,250 feet above sea level is the world's second highest mountain. A lawyer and a physicist, members of an unsuccessful expedition to climb the peak, are trapped on the ledge, a space roughly 4 1/2 feet by 8 feet.

The stage mountain rises 43 feet, 6 inches from under the stage of the Kreeger Theater to within two feet of the grid, seven feet higher than any previous Kreeger set. Technical director David Glenn, master carpenter Jim Glendinning and the crew made the mountain of Styrofoam blocks, which they sculpted with hot wire and dripped acetone. It was made in the workshop in 8-by-16 foot sections and assembled onstage, a technique they were all familiar with from last winter's production of "A Midsummer Night's Dream."

"This was sort of like the Midsummer set on edge," Glendinning said.

"The director and the designer decided right away that they wanted a realistic set, as opposed to a stylized white set or something," said associate producer Nancy Quinn. "At that point it was a question of what materials to use."

Designer Ming Cho Lee had planned each curve and cranny of the ice, made to look ice-like with tissue paper coated with clear glazed paints. The sections were glued together and fastened to wooden platforms that are visible only from backstage. The sections that are to be climbed were reinforced with dense foam rubber to withstand the gouges of the climbing equipment the actors will use.

But how do you make an avalanche? Evoking reality through two senses: sight and sound. The physical elements are plastic snow and chunks of Styrofoam, let loose from a bag attached to the grid. Sound technician Jay Rosenberg created the sound by taking a recording of an avalanche, playing it at half speed, making another track by playing it through a filter, then mixing them all to produce a frightening rumble that builds to a loud roar and then diminishes to an eerie whoosh. Incidentally, the avalanche should go safely into the pit, not the audience. Technicians retrieve the snow after every performance so it can be used again.

Just as the avalanche would be incomplete without the sound, the mountain would not look like ice without the right light. Allen Lee Hughes' lighting design was not the problem. Getting to the grid to put up and focus the lights was, since the floor space, on which ladders would normally be placed, was either taken up by the mountain or removed for the pit. Master electrician Nancy Shertler was hoisted to the ceiling strapped in a bosun's chair to do it. "It took twice as long as it would normally," she said.

Shertler's other task was to invent an appropriate cloud that would hang over the pit, below the ledge. "There is only one good fog product," she said. "But it has a tendency to go up in the air and head for the person most likely to sneeze. We think that putting some dry ice in front of the fog machine will do it."

There is, of course, the question of safety. The pit, a 16-foot drop, is lined with boxes covered with tumbling mats. As a precaution, ropes used in mountain climbing will be replaced regularly. A technician, Ron Boardman, who is an amateur mountain climber, has been giving climbing instructions to the cast, and no climbing will be done without safety lines. In fact, it seems that the technicians, rather than the actors, were in danger.

Shaping the Styrofoam with acetone exposed the carpenters to toxic fumes that gave them "humongous headaches," said electronics consultant Grafton Cole. And there were no safety lines or padded pits while they were constructing the mountain. "These guys literally put their lives on the line," he said.