As Tommy Caldwell and Kevin Jorgeson near the summit of Yosemite's Dawn Wall, we asked renowned climbers Lynn Hill and Jimmy Chin (who took this photo) for their insights into the hardest big wall free climbs.

Hill made the first free ascent of the nearby face known as The Nose in 1993, and then climbed it in just a day in 1994. Chin, who has made first ascents on big walls in Pakistan and India, photographed climbing in Yosemite in a 2012 National Geographic spread.

Just as the current Dawn Wall project had been considered too difficult to ever be free-climbed, the future of the sport lies in what today seems unfathomable.

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