Every year millions of people visit the National Parks in the United States. Families go to camp for the weekend, hikers and backpackers set out to explore the wilds of this country, photographers seek to capture the beautiful scenery of nature.  But some people will never come out of the parks and become lost in the wilderness. Many are never heard from again and no one knows exactly how many people are missing to this day in our National Parks.  Many of the cases are explainable, but there are also those that don't make much sense with the information we have.  The disappearances of Dennis Martin, Bobby Bizup and Charles McCullar are three of those cases.