In the United States National Park System alone there are more than 84 million acres (340,000 square kilometers) of preserved woods, deserts, mountains and other wilderness, so it's no surprise that in the past 100 years there have been a number of cases of hikers going missing [source: National Park Service]. Many of those who vanished were young children and inexperienced hikers, but some were healthy and seasoned outdoorspeople. But is there more to these disappearances than just kids wandering off, or hikers becoming disoriented?
What could cause someone to seemingly vanish into thin air? There are two approaches people take to explaining these mysterious disappearances: earthly and supernatural. Most hiking experts would say that these missing hikers made common mistakes like taking on more than they could handle or failing to time their turnback to beat the sunset [source: Stevenson]. The disappearances have become a focus for urban legend, online message boards and non-fiction books; "Missing 411" author David Paulides thinks something more intriguing is afoot. His book examines more than 1,100 cases of people mysteriously vanishing from United States parks [source: Hiltner].
Let's be honest – although it might be fun to imagine monsters or something spookier, no proof for any supernatural disappearance has ever been provided. But there have definitely been some unexplained disappearances both in the United States and abroad - in formal, federal government-run National Parks as well as in related spaces like National Forests, recreation areas, state parks and more. These are 10 of the most fascinating; let's start in the early 20th century and move up to the present.