Even if you're accustomed to running at elevation, ascending 8,000 vertical feet during the first half of the Pikes Peak Marathon will likely rattle your guts, leave you gasping, and humble your ego. Traversing over boulders and rocky trails above the tree line is tricky enough but the unpredictable weather can bring several inches of snow, even if temperatures at the start were in the 50s. At 12,000 feet, it can take a frustratingly long time to cover just one mile; 2012 champ and mountain running superstar Kilian Jornet finished the event in 3:40. If the thin air doesn't make you dizzy, the descent, littered with roots and rocks, just might.