It is one of the world's most difficult climbs - but may soon be impossible. Mountaineers are being warned that the North Face of the Eiger has become too dangerous to attempt because its ice fields are melting.
Guides working on the 13,000ft-high mountain in the Swiss Alps say that a combination of last summer's heatwave and poor snowfall since has caused a loosening of the permafrost that holds the rockface together.
The result is that the North Face, which has claimed more than 60 lives since the first successful ascent in 1938, is "falling apart", leaving climbers at severe risk of being injured or killed by falling rock and ice.
Hans Ulei, 38, a mountain guide from the nearby town of Interlaken, said: "We are telling people, 'Don't go on the North Face'. It is too dangerous.
"The mountain is falling down. These days I am often woken in the night by a sound like thunder. At 5am recently I heard that noise and when I looked from my window the North Face was half obscured by a grey cloud of powder from broken rocks."
A spokesman for the Swiss Alpine Club said that recent climatic developments have made the 1938 route up the North Face too dangerous. "My advice to anyone contemplating the Eiger is not to try the North Face.
"The conditions mean you will have a much higher chance of getting knocked out by rock or ice fall. There are many other routes up the mountain and the straightforward rock-climbing actually improves when the temperature goes up."
The North Face, or Nordwand, is 6,000ft high and has long been regarded as the "ultimate" challenge by those attracted to its cruel beauty: a vertical mile of shattered limestone rock and polished ice fields on a mountain known locally as the Eigerwand, or "Eiger wall".
It is regarded with awe by climbers, for whom its deep fascination was heightened by the 1975 spy film, The Eiger Sanction, in which Clint Eastwood played a rock-climbing assassin hired to kill a fellow mountaineer.
Joe Simpson, the author of Touching The Void, a best-selling book about the adventures of two climbers that has been made into a successful film, wrote about the Eiger in a previous book, The Beckoning Silence.
For the past century, Mr Simpson said that "it has been the climb that has defined extreme mountaineering". "For over 60 years it has killed some of the finest climbers of their generation. And for those brave enough to attempt the face there is the added weight of its tragic history," he wrote.
The first successful assault on the Eiger was made in 1938 when Heinrich Harrer and Fritz Kasparek, Anderl Heckmair and Ludwig Vorg climbed into history.
They became national heroes in Austria and Germany, and although Hitler subsequently claimed the ascent as a triumph for the Aryan race, there was a vitriolic disagreement within the group over the way their feat was used for propaganda.
Subsequent dramas on the mountain have included Sir Chris Bonington's first successful British attempt in 1962, during which he and his climbing partner, Don Whillans, rescued another British climber, Brian Nally, after his partner, Barry Brewster, was killed by falling rocks.
James Edwards, 28, a British teacher who attempted the climb at Easter, said that the conditions had made it impossible even to consider an ascent. "I spoke to two very experienced guys who had already made an attempt and they had had to turn back after 500 metres because there were rocks and stuff coming down on them."
Marc Ziegler, one of the mountain rescue team for the North Face, said: "Things are certainly changing. The first ice field doesn't exist any more and the second and third are getting much smaller."
Dr Rolf Burki, a lecturer at Zurich University who produced a recent study for the United Nation's Environment Programme on the changes occurring in the Alps, said that warmer weather was to blame for the difficulties.
Temperatures on the mountain have increased by one degree Celsius since 1850, but were now rising more rapidly, with a projected warming of 1.5 to 5.9 degrees during the next century. "In that area of the Alps there is a great problem because of retreating glaciers and melting permafrost. A lot of the climbing routes that have been possible in the past will not be possible in the future because of rockfall," he said.