Up at dawn, they lie chilled and cramped on a ledge hundreds of metres above ground. Their bodies are sore, the skin on their hands shredded.
Water is the first thing they reach for, as dehydration can kill. A bag of their waste is close by, the smell masked by cat litter and baking soda. They have to be careful not to risk running out of supplies.
But they also know they cannot afford to rush and lose focus - a wrong move could kill.
This is the world of climbers Cheang Qing Xin, 32, and Kelly Khiew, 30. The husband and wife are believed to be the first Singaporeans to scale the 915m El Capitan rock wall at Yosemite National Park in California.
"Fewer people summit El Capitan in a year than Mount Everest," says Mr Cheang. "Each climb takes about four to five days. They are a serious commitment. There are no porters to carry your gear - which could weigh 30-50kg."
Last month, two climbers made news around the world by being the first to "free climb" one of El Capitan's toughest sections, the Dawn Wall. They ascended the natural rock features without aid, using only ropes and other gear employed to arrest falls.
Mr Cheang and his wife have scaled two sections of El Capitan, The Nose and Salathe Wall, half by free climbing, half using aid. They have yet to attempt the Dawn Wall.
Two years ago, he left a career in the Singapore Armed Forces and she quit her job as a museum manager to pursue their shared passion.
They formed QX Adventures in 2013 to provide guiding services for some of the world's toughest climbs in places such as Taiwan, Thailand and the United States.
He began climbing in the army and his wife while in junior college. As big-wall climbers, they must figure out the best way to get up a wall as they go along. Instead of clipping the rope secured to their harnesses into ready bolts, they place pieces of protective gear into cracks that they find.
Resting spots are often just wide enough to lie flat on. Some are "small enough for you to roll off the edge if you aren't careful", said Mr Cheang.
The risks are high, but the couple found it even more of a gamble to change their lifestyles completely. They made the choice after their first El Capitan ascent in 2011.
No one took up the big-wall climbing programmes at QX Adventures in its first year. But last year, two groups signed on, and two months into this year, the company already has eight clients lined up.
They have also secured gear sponsorship, and even though money is tight, they have no regrets. Their commitment has already earned them respect within the climbing community.
Engineer and veteran climber Ng Chin Seng said: "They are walking way off the beaten path and enjoying it."
Ms Khiew said: "I've learnt so much from climbing. Live within your means. Identify the must-haves, do away with the good-to-haves. Accept and manage fear - don't be misled by it."
This article was first published on Mar 2, 2015.
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