Rachel Flowers Harwell shared this awesome tip
Check out the National Parks website, they are offering a free annual pass to active duty military personnel and their dependents: http://www.nps.gov/findapark/passes.htm
Here are the details:
Free Annual Pass for Military
- For active duty military personnel and dependents with proper identification (CAC Card or DD Form 1173)
- May be obtained starting on May 19, 2012.
Frequently Asked Questions about the Annual Pass for Military