Two climbers have spent the past 19 days clinging to a granite cliff a kilometre tall in an attempt to complete the world's first free climb of El Capitan.
Kevin Jorgeson, 30, and Tommy Caldwell, 36, could make the final push for the 3,000 foot (914 metre) summit in California's Yosemite National Park later today.
They are free climbing, meaning that they are using ropes only to prevent a fall and not to aid ascent.
Their ascent has been gruelling for both climbers who were delayed by repeatedly cutting their fingers on razor-thin holds in the rock face.
On Friday, Jorgeson wrote this triumphant post on his Facebook page after cracking a particularly tough section:
The pair left ground level on 28th December, with Jorgeson telling friends of Facebook: "Today we started our push! It may be a few weeks before we walk on flat ground again, but we are psyched."
As well as spending every hour of every day in the elements, they also sleep on the rock face in tents suspended from metal pegs.
Kevin Jorgeson made this video diary showing what conditions in the tent can be like:
Caldwell has been making faster progress than his climbing partner Jorgeson, who was forced to rest for two days after his fingers were badly cut.
A spokeswoman for the pair said that Jorgeson is now catching up and that the pair hoped to make the final push together.
El Capitan is the largest granite monolith in the world and was first conquered by climbers in 1958.
There are about 100 different routes to the summit, but Jorgeson and Caldwell are attempting the most challenging one known as Dawn Wall.
If they succeed, it will be the world's first free climb of Dawn Wall.