On January 14, 2015, Tommy Caldwell pulled himself atop Yosemite National Park’s El Capitan, completing the first free ascent (meaning he used ropes to protect himself during falls but not to aid his upward progress) of the granite monolith’s most difficult route. For the previous six years, the Estes Park native had devoted much of his time to conquering El Capitan’s Dawn Wall, a 3,000-foot vertical swath of almost featureless rock. In his memoir, The Push, out May 16, Caldwell recounts how his entire life prepared him for what experts have called one of the most challenging free climbs in history. Here are some of the highlights.

Tommy Caldwell reflects on his life as a renowned climber in his new memoir. Photo by Jimmy Chin.

At a young age, Caldwell is mesmerized by the legendary climbers who pass through his hometown of Estes Park en route to the Rocky Mountains.

The Diamond on Longs Peak. Image Courtesy of IStock

Twelve-year-old Caldwell becomes the youngest person ever to climb the Diamond, a 950-foot alpine wall on Longs Peak.

After a summerlong climbing road trip with his dad, Caldwell enters his first professional climbing contest—the Outdoor Sports Festival in Snowbird, Utah—at age 16. He wins, gaining widespread recognition from climbing media.

Caldwell joins his then girlfriend, renowned climber Beth Rodden, on an expedition to Kyrgyzstan. They’re captured by a Taliban-affiliated group and held hostage for six days.

Caldwell cuts off two-thirds of his left index finger while using a table saw. Within months, he free-climbs the extremely technical Salathé Wall on El Capitan in less than 24 hours.

Caldwell completes Flex Luthor (rated 5.15a, the highest grade in U.S. rock climbing) in Fortress of Solitude, a climbing area near Rifle.

As he continues to master increasingly difficult routes, Caldwell ratchets up his training regimen with intense cardio and weight-lifting sessions.

Cerro Fitz Roy in Patagonia. Courtesy of Wikipedia

On Caldwell’s first trip to Patagonia, he free-climbs Cerro Fitz Roy, a demanding peak only a handful of elite alpinists ascend each year.

After a painful divorce from Rodden and estrangement from his father, a devastated Caldwell decides to attempt the Dawn Wall—a feat that was thought to be impossible. “I didn’t know what else to do, so when the late autumn winds began to rip down off the Rockies I returned to El Capitan. Beating my head against the Dawn Wall became my beacon in the night,” reflects Caldwell in The Push.

In less than 24 hours, Caldwell and free-solo specialist Alex Honnold climb Mt. Watkins, El Capitan, and Half Dome—three of Yosemite’s most iconic and largest formations—to achieve an unprecedented feat of free climbing.

Caldwell and Honnold summit Cerro Fitz Roy and the six peaks nearby in just four days. (This ridgeline is depicted in Patagonia’s familiar logo.) The pair become the first to link all 4,000-plus vertical meters and do so using minimal gear.

It takes Caldwell six years to master the Dawn Wall’s crux—the most difficult section of the climb—located in the 15th pitch. When he finally completes the 10-move sequence, it’s through what he refers to as an out-of-body experience: “Like an outside observer, I watch myself glide across the rock, left arm high, two-finger hold, hips in, scoot right foot beneath me. Flow, the state of optimal experience in which one feels fully engaged, is one of the most magical experiences a person can have.”