Want to get outdoors this weekend and enjoy the cooler fall weather that's been setting in? Try a national park — they're all free on Saturday (Sept. 29) for National Public Lands Day.

The fee-free day has been declared by the National Park Service, U.S. Fish and Wildlife Service, U.S. Forest Service and the Bureau of Land Management for the parks and other properties they oversee.

The National Park Service also waives park entrance fees on June 9 (Get Outdoors Day) and during National Park Week (April 21-29). Though entrance to parks will be free, there might still be charges for camping and other facilities.

Some of the national parks participating in the fee-free day include Denali National Park in Alaska, Death Valley National Park in California, Everglades National Park in Florida and Shenandoah National Park in Virginia.

National Public Lands Day is also a day when some 170,000 volunteers are expected to help out at more than 2,100 sites. Last year, volunteers contributed an estimated $17 million with their time by helping to plant about 100,000 trees and other native plants and building and maintaining some 1,500 miles of trails, according to a release from the National Environmental Education Foundation, which runs the Public Lands Day program.

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