High-altitude mountain running, also known as skyrunning, is one of the most challenging settings for a runner to compete in. It’s also one of the most scenic.

According to the International Skyrunning Federation, skyrunning is defined as mountain running up to or exceeding 2,000 meters (about 6,500 feet) where the incline exceeds 30 percent and the climbing difficulty does not exceed 11-degree grade.

CNN recently followed Swedish runner Emelie Forsberg as she discusses the art of skyrunning and what drives her to ascend and descend such daunting peaks—and the mental challenges she has to overcome in the process. The video is below.

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