The seeds of the 2021 “Lost World Expedition” were planted more than 20 years ago. At that time, my life revolved around new routes on the great walls of the world, but it began to dawn on me that expedition climbing can be a selfish pursuit. As I wondered if my skills as a climber and guide could be used for something more meaningful than first ascents, someone at National Geographic introduced me to Dr. Bruce Means. Means, a conservation biologist who specializes in documenting biodiversity in the tepui region of northern South America, needed someone to help him access tough terrain in Guyana’s Pakaraima Mountains. I was a guy who could do just that.

In 2003, we spent a few weeks searching for new frog species in the cloud forest below the northern prow of Mt. Roraima. After Bruce flew home in a helicopter, John Catto, Jared Ogden, and I established a new route on the Prow, coming within a move or two of its first free ascent (AAJ 2004). Jared, Greg Child, Rob Raker, and I returned with Bruce in 2006, again finding more new species and establishing a new route on Roraima’s east face (AAJ 2007). While flying home in the helicopter, we passed over a small tepui that wasn’t on our map. Its summit was incised by a 600’-deep sinkhole with a thick forest in its bottom. Bruce grabbed me by the shirt and shouted, “Mark, I need to be in that hole.” He called it “a lost world within a lost world.”

In 2012, Bruce and I were helicoptered to the top of that tepui, called Weiasspiu (a.k.a., Wei-Assipu, 7,035’, 5°13'22"N, 60°42'09"W), about one mile east of Roraima on the Guyana-Brazil border. I lowered us into the hole where Bruce searched for a frog that he called a “missing link” in tepui evolutionary biology. On his fifth day in the hole, he found it: a species of pebble toad now called Oreophrynella weiassipuensis.

For years, Bruce had been trying to understand—much like Darwin had with his finches in the Galapagos—how endemic species of amphibians and reptiles living on tepui summits got there. Did they become isolated on these islands in the sky millions of years ago as the sides eroded away? Or did frogs and lizards climb up these wild cliffs, propelled, perhaps, by some innate desire to explore their world? By comparing mutations in the weiassipuensis’ DNA to its closest ancestor, Bruce proposed the species diverged tens of thousands of years ago, not millions, as most scientists expected. This suggests weiassipuensis may have climbed up (and down) the sheer walls of the tepui.

To further study this hypothesis and others, Bruce proposed an expedition that would follow an elevational transect through the heart of the Paikwa River basin, culminating with the first ascent of Weiassipu’s walls. According to my research, the only previous expedition to explore the headwaters of the Paikwa River was a British team in the late 1960s. In 32 previous tepui expeditions, Bruce had never studied the ecosystems on the vertical walls. As far as he knew, no one had. To help bring Bruce, who would turn 80 on this expedition, ascend a big-wall rock climb, I recruited two ringers: American Alex Honnold and Federico “Fuco” Pisani, a Venezuelan who is one of the world’s most experienced tepui climbers. According to Fuco, Weiassipu might have been one of the last unclimbed tepuis.

On February 7, 2021, we flew to the remote village of Phillipai, along with a filmmaking team. We loaded our equipment into handmade dugout canoes with outboard motors and proceeded 20 miles south via the Kukui and Ataro rivers to the tiny village of Wayalayeng. From here, we set off on a 40-mile trek across a swampy floodplain to the east of the Pakaraima Mountains, accompanied by 70 Akawaio porters and guides. It rained incessantly on the trek, and Bruce fell dozens of times. His safety soon became an ever-present worry for our team.

A week later, we established a base camp beneath a 200’ waterfall called Double Drop Falls. Bruce and I had been to Double Drop twice before but had never explored the mysterious horseshoe valley to the south that lay between us and the base of Weiassipu’s north face. Bruce needed time to recover from the trek, so we decided to split up. The climbing team would move ahead to find a route to the base of Weiassipu, about five miles away, while Bruce stayed behind to collect specimens.

A group of Akawaios, including Troy Henry and Edward Jameson, who climbed the Prow with a British expedition in 2019 (AAJ 2020), led us into the valley. They slashed a path with their machetes through giant ferns and past old-growth trees held fast in the thin, sandy soil by colossal buttress roots. On our second day out from base camp, the ground steepened, and we entered a maze of jumbled, greasy boulders cloaked in a thick blanket of moss. The firm earth gradually gave way to a lattice of deadfall that would occasionally break free like a trap door. When we finally popped out of the forest at the base of Weiassipu, it felt like being born.

The north face of Weiassipu is about 1,000’ tall, split by a massive, vegetated ledge system 700’ up. Our line followed a meandering path through bulletproof, horizontally banded quartzite on the 700’ lower wall. (The 300’ headwall above the ledge remains for future ascensionists.) We swapped leads and fixed ropes behind us so that we could haul Bruce up later. But when we got back to our hammock camp at the base of the wall on day three, we learned that our expedition doctor had pulled the plug on this hair-brained scheme: Bruce, who turned 80 on our expedition, would go no further. Instead, Bruce provided us with a drawing of a frog from the genus Stefania that he hoped we might find on the summit, one that likely followed a different evolutionary path than weiassipuensis. If we could find this frog, Bruce would be one step closer to understanding how life evolved on tepuis.

The next day, Alex repointed our six-pitch route, The Sloth Wall (700’, 5.12b), eliminating the few moves of A0 we had used previously. We had placed 13 bolts, including anchor bolts and one piton and one bolt to protect the crux, a 25’ roof on pitch two. We established a camp on the ledge system, and the next morning we completed a 300’ rising traverse up the ledge (to the southwest), fighting our way through strangle-thick vegetation to reach the summit plateau. Alex disappeared shortly after topping out, and Fuco and I spent the rest of the day searching unsuccessfully for frogs. Back at our portaledge camp that evening, Alex suddenly reappeared, barefoot, holding a pair of rock shoes in his chalk-covered hands. He had just free soloed our route in about 45 minutes. Fuco said it was the first free solo of a tepui.

We reunited with Bruce two days later. He was disappointed that we hadn't found the Stefania or any other amphibians on top of the tepui, but staying behind had been a blessing in disguise. At the time of this writing, DNA analysis has tentatively confirmed that Bruce discovered six new species in the cloud forest below Weiassipu, including a cousin of the Stefania, a nonvenomous member of the Bothrops genus of snakes, and a spectacled lizard with a transparent lower eyelid. For decades, Bruce has nurtured a quiet dream that one day he might find a creature in the Paikwa River basin so rare and singularly beautiful that the Guyanese government would finally conserve this area as a national park. “Now,” he says, “it’s up to someone else to pick up where I’ve left off.”

More information about this expedition can be found in the April 2022 issue of National Geographic magazine. Parts of this report were adapted from that article.