evidence: Climbing Everest. Without Oxygen. In Winter. [...] In the long history of climbing on Mount Everest, there have been only a handful of summits during winter. And just one person—Ang Rita Sherpa—has climbed the world’s highest peak in the off-season without the use of supplemental oxygen. This winter, Basque climber Alex Txikon aims to become the second. [...] Polish climbers Krzysztof Wielicki and Leszek Cichy made the first winter ascent of Everest on February 17, 1980. Since then, 13 others have managed to reach the summit during that season, although eight of those occurred before December 21. Ang Rita Sherpa made his ascent without the use of bottled oxygen on December 22, 1987, just one day into the winter season, which means the bulk of the climbing and acclimatization actually took place during fall. No one has made a winter ascent since 1993.