PHILADELPHIA (CBS) – The weather will be perfect this weekend to head outdoors to visit a national park, especially since it’s free starting tomorrow.

The National Parks Service is turning 100 years old and they waived all entrance fees as part of National Park Week.

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“It’s about making great connections, exploring amazing places, discovering open spaces, enjoying affordable vacations, and enhancing America’s best idea—the national parks,” according to the National Park Service.

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Only a third of the 411 national parks actually have entrance fees, but those that do tend to be the biggest attractions, like the Grand Canyon.

The fee waiver includes entrance fees, commercial tour fees, and transportation entrance fees. Other fees such as reservation, camping, tours, concession and fees collected by third parties are not included unless stated otherwise.

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National Park Week is April 16th through the 24th.