On Sunday, access to all 490 National Parks in the United States is free in honor of Veteran’s Day. This year, the federal holiday marks 100 years since the end of World War I was officially declared on the 11th hour of the 11th day of the 11th month. Several national park locations have strong ties to the holiday thanks to their American military history, from the USS Arizona Memorial at Pearl Harbor to the Little Bighorn Battlefield in Montana.

Yellowstone, the world’s first national park, was established in 1872, and called upon the U.S. Calvary to serve as the location’s first park rangers. Located in Wyoming, Montana, and Idaho, the 3,468.4 square miles that make up the wilderness recreation area boast a geothermal geyser that recently spewed decades-old trash and the remarkably colorful Grand Prismatic Spring.

Multiple parks have served as training grounds for troops over the years, so locations have both birthed and commemorated the ends of American military careers. World War I created a need to use open space in this way: African-American Buffalo Soldiers trained at Hopewell Culture National Park in Ohio, and future president Dwight D. Eisenhower led a tank school on the grounds of the Gettysburg Battlefield in preparation. On November 13, 1982, the Vietnam Veterans Memorial, a design featuring two black granite walls that originally listed 57,939 names of servicemen, was dedicated in Washington D.C.

A 1918 photograph of soldiers at Camp Colt, Eisenhower’s group of tank soldiers trained on the Gettysburg battlefield. Public Domain

With all of the varied national park options across the country, tracking visits to them can be difficult. National Park passports, designed specifically for domestic travel and first introduced in 1986, can make marking off these historic sites more satisfying. For some folks, acquiring stamps in these passport-lites is almost an obsessive fixation; the National Park Travelers Club, founded in 2004, has more than 2,000 members. Organized by geographic region, the passports are filled with maps and park information, making America’s database of parks and historic sites highly accessible. Free park days, like Sunday’s, work to lower the barrier of entry for people to enjoy the nation’s beauty, too.

Special World War I events this weekend include the Chickamauga and Chattanooga National Military Park in Georgia and Tennessee hosting a caravan tour that explores the fort’s military relationship to the First World War, and a park ranger at the Second Bank of the U.S. leading a discussion on how the war affected Philadelphia.