Got the end of summer blues? Looking for one more outdoor adventure before the kids go back to school?

You're in luck! The National Park Service is offering free admissions at all of its sites Friday in celebration of its 101st birthday.

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Whether it's one of the Park Service's' most popular sites, or a hidden gem, the parks will be totally free to roam around and enjoy the last bit of summer.

Don't have time during the day? Here's a look at some of the most spectacular photos taken on our National Parks.