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The U.S. Geological Survey offers a Lifetime National Parks Pass for Senior Citizens (age 62 or above) for $10. To get this price, you'll need to purchase it in person at one of these locations. It grants access to all 417 national parks and over 2,000 other recreation areas. Deal ends permanently on August 27.

Alternatively, you can buy one online for $20 plus $5 for shipping.