They’re having a birthday-- and it's a big one. The National Park Service turns 100 on Aug. 25 and parks around the country are celebrating the milestone. Starting Thursday, entrance to the 124 parks that usually charge admission is free through Sunday (Aug. 28). Throughout the nation, special events at over 400 parks will celebrate the centennial. From birthday cakes and cupcakes to special classes and programs, most parks have something special planned. National parks may be synonymous with camping and hiking today but Americans haven't always been able to enjoy these protected lands. The story of the national...