Principal photography began on August 12, 1974 in Grindelwald, Switzerland, with a team of climbing experts and advisers from the United States, Canada, Germany, Switzerland, and the United Kingdom. The climbers were based at the Hotel Bellevue des Alpes at Kleine Scheidegg, located below and between the Eiger and Lauberhorn peaks in the Bernese Oberland region. At in elevation, the north face of the Eiger, which means ogre in German, is renowned for its treacherous climbing, earning the German nickname Mordwand or murder wall. By 1974, forty-one climbers had lost their lives trying to climb the forbidding edifice. Eastwood decided to take on the most dangerous work during the first two days of shooting. By midafternoon on August 13, as light began to fail, a wrap was called after shooting a rock slide sequence. While the team was preparing to be helicoptered off the north face, Hoover remembered they had not taken any footage from the climbers' point of view of the boulders crashing down on them. With his handheld camera, Hoover and twenty-six-year-old British climber David Knowles rappelled down to the ledge and took the needed footage. As they were gathering their gear, a huge rock broke free and smashed into the climbers, killing Knowles and leaving Hoover with a fractured pelvis and severely bruised muscles. Following an impromptu wake for Knowles, Eastwood considered canceling the production, but the climbers persuaded him to continue on, assuring him that they all knew the risks of their trade and did not want Knowles' death to be meaningless.