This year, the U.S. National Park Service turns 100. American's 28th President, Woodrow Wilson, formed the National Park Service in 1916 to "protect the wild and wonderful landscapes" in the United States.

Today, the organization manages nearly 34 million hectares of land.

The organization is celebrating all year long. And starting April 16, the National Park Service will also be celebrating National Park Week.

The National Park Service manages more than 400 national parks, historic sites, monuments and more. There are 127 national parks that usually charge visitors admission. Visitors to Arches National Park in Utah, for example, pay $25 per car. The Grand Canyon National Park in Arizona charges $30 per car.

But during National Park Week, visitors can enter all national parks across the country free of charge. National Park week this year runs from April 16 to April 24. Earth Day is also celebrated during National Park Week, on April 22. The National Park Service urges people to volunteer at nearby national parks on that day.

To celebrate the start of National Park Week, here are some fun facts:

The National Park Service started 100 years ago, but some parks are over 100 years old. Yellowstone National Park in the western United States was established in 1872 as the first national park in the America. It was also the world's first national park.

Each of America's 50 states has at least one location managed by the park service. The largest park is the Wrangell-St. Elias National Park and Preserve in Alaska. It covers more than 5 million hectares of land. Alaska is also the state with the most national parks.

The smallest National Park Service site is the Thaddeus Kosciuszko National Memorial in Philadelphia, Pennsylvania. The memorial honors Kosciuszko, a Polish freedom fighter who designed defense walls during the American Revolutionary War.

The newest National Park Service site is not far from us here at the Voice of America. It is the Belmont-Paul Women's Equality National Monument in Washington, DC. The site is an historic house and museum on Capitol Hill. It honors women's right to vote and equal rights in America. It became a part of the National Park Service this year on April 12.

Over 300 million people visited U.S. national parks last year. That was a 5 percent increase compared to 2014.

Will you be one of the visitors this year?

I'm Dan Friedell.

Dan Friedell adapted this story for Learning English. Ashley Thompson was the editor.