National parks aren't theme parks. There are no safety belts or security guards, no sanitized lazy rivers or glove-waving costumed creatures. But there is excitement aplenty in our nation's wild protected parkland. Death-defying clifftop switchbacks, fuming volcanoes, and frothy waterfalls will make the most scream-inducing thrill rides seem like cherry pie. So summon your courage and head to one of these 10 pulse-quickening national park trails, where perilous paths lead to daredevil, once-in-a-lifetime adventures.