flickr/Yellowstone National Park

On Tuesday, August 25, the National Parks Service turns 99. If you are near a national park, you should probably head that way—because all the parks are offering free admission to commemorate the occasion. Otherwise take a few minutes to wax nostalgic on all the good times people have had at national parks since the NPS came into being in 1916.

There are 408 national parks, with at least one in every state. The largest is Wrangell-St. Elias National Park and Preserve in Alaska, at 13.2 million acres, while the smallest, Thaddeus Kosciuszko National Memorial, in Pennsylvania, clocks in at 0.02 acres. Yellowstone National Park, established in 1872, was the world's first true national park.

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