ver Cuevana 3. More people have traveled to space than have summited K2, the world’s second-highest peak that’s considered by many to be the Earth’s most challenging climb. Breathtaking: K2 follows seasoned climbers Carla Perez and Adrian Ballinger as they attempt summiting “the savage mountain” without the aid of supplemental oxygen — an expedition fraught with challenges that threaten not only their chance to reach the top, but also their lives.