El Capitan is massive - 3,000 feet (900 meters) high, the world's largest granite monolith. Hang out at the first El Cap overlook just inside Yosemite Valley and you'll see car after car full of people driving past with their chins on the dashboard, because that's the only way they can see the top of this behemoth. (If you're a pedestrian here, it's best not to rely on drivers spotting you as you cross the road.) El Capitan is also tough - made from granite formed miles underground and slowly cooled, emerging so strong that not even the glacier that carved out Yosemite Valley could shift it.
It's also one of the world's premier rock-climbing destinations. On any summer day you'll find crowds of people in El Capitan Meadow training their binoculars on the climbers on the wall. It's usually a two or three day climb from Yosemite Valley to the summit, so in the evening the climbers hang brightly colored hammocks off the cliffside and settle in for the night with nothing between them and the valley floor but a few thousand feet of air and a couple millimeters of reinforced nylon. No sleepwalker, it is believed, has ever successfully scaled El Capitan.