Half Dome, one of the most iconic features in our national park system, sits at an elevation of 8842 feet, and requires a 14.2-mile round trip hike to reach the summit via the Mist Trail. To assist climbers up the final 400 vertical feet, steel cables were bolted into the granite rock face by the Sierra Club in 1919. You can check out a pretty awesome photo of what it's like to climb the cables here.
A 2008 article in Backpacker Magazine stated that the Mist Trail sees 2,500 to 3,000 people per day during summer weekends. Over the years several people have fallen to their deaths along the route. In response to the heavy use of the trail, the park announced earlier this year that they will be implementing a new permit system for climbing the monolith:
Applications for permits to hike the trail are available from March 1 through March 31, 2013. The park will allocate permits through a preseason lottery, a two-day in advance lottery, and as part of the Wilderness Permit process (daily lottery). Details regarding the lotteries and the wilderness process can be found at the park's website. The lottery will be conducted through www.recreation.gov.