At the narrow entrance to the Persian Gulf, the jagged limestone walls of the Musandam Peninsula, in Oman, form a deepwater soloing oasis. Rock climber Alex Honnold – the only person ever to free-climb Yosemite's three biggest walls in one day – and world-class adventure photographer Jimmy Chin toured the coast's fjord-like waterways on a 45-foot catamaran, taking day trips by Zodiac to the sun-baked rock formations that rise out of 80-degree seawater.

"I'm sure we did more than 10 first ascents," says Chin, of the three weeks they spent exploring the coastline. "We climbed a spire that had to be 700 feet," says Honnold. "You could see schools of tuna jumping in the distance, flying fish skirting the surface – I even saw a sea turtle as big as a man." Climbing horizontally on deteriorating overhangs, though, made for some harrowing moments.

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"Your feet could hit the bottom of the ocean if it wasn't high tide," Honnold says. At one point, he narrowly avoided an encounter with a venomous lionfish: "It was just lurking there beneath me." During one early morning scramble, he stumbled upon a plateau littered with 500-year-old ruins. "It felt like I had discovered an ancient civilization," he says.