It's a great deal to visit the great outdoors.
Active-duty troops and their families can get a http://store.usgs.gov/pass/military.html">free military version of the America the Beautiful National Parks and Federal Recreation Lands Annual Pass. Part of the White House's Joining Forces initiative, the pass costs $80 for civilians.
The pass is accepted at all sites run by the National Park Service, U.S. Fish and Wildlife Service, Bureau of Reclamation, Bureau of Land Management, U.S. Forest Service and U.S. Army Corps of Engineers locations.
Better yet, friends can come along for free, too. The pass is good for any accompanying passengers in areas that charge per vehicle; or the pass owner and up to an additional three adults at sites that charge per person.
You can pick one up at any national park or wildlife refuge that normally charges an entrance fee.