Hundreds of climbers are attempting to scale Mount Everest despite an unstable ice block dangerously hanging over the key trail, high travel costs and increased permit fees.

Around 492 climbers and an equal number of Nepali climbing guides are gearing up for the ascent to the 8,849-meter (29,032-foot) high summit this month during the much-anticipated window of good weather on the world’s highest mountain.

Climbers began gathering in April at the base camp, which is at an altitude of 5,300 meters (17,340 feet.) But for more than two weeks a massive and unstable block of ice, or serac, stalled them from moving further up the peak.

The serac is part of the Khumbu Icefall, a constantly shifting glacier with deep crevasses and huge pieces of overhanging ice that can be as big as a 10-story building. The section is considered one of the most difficult and trickiest to climb.

Ang Tshering Sherpa, a mountaineering expert in Nepal, said there are a good number of climbers on Mount Everest this season despite the Iran war and increased travel costs. The number of climbers from the U.S. and European countries has decreased, but there has been a rise in the number of Asian climbers.

Mount Everest straddles the Nepal-China border, although China has closed its route this year, leaving climbers to make their attempts from Nepal on the south side.