Big birthdays can be tough to plan, from deciding how to have fun and satisfy competing friend groups, to crafting party invitations that tactfully say, "No, I am not too old for presents." But the National Park Service, which will celebrate its centennial on Aug. 25, knows there’s only one way to ensure a flawless birthday bash: Don’t leave anyone out. Which is why, starting on April 16, the bureau is partnering with the National Park Foundation to host National Parks Week, when every national park will be open to the public, free of charge. The celebration, which will continue through April 24, is America's largest celebration of national heritage.

"National parks represent the very best of America,” said Midwest Regional Director Cam Sholly. “The great opportunities planned for National Park Week will provide extra incentive for people to visit a national park during this year's centennial celebration; parks that normally charge entrance fees will waive them for the entire week so that everyone has a chance to visit.”

Other highlights throughout the week will include fun programs for kids on Junior Ranger Day, volunteer projects on Earth Day (April 20), national park meetups where community members can gather to take pictures and videos to post to Instagram (called an InstaMeet) and recreational activities on Park Rx Day.

“With special events like Junior Ranger Day,” Sholly said, “we invite the next generation to discover our nation's treasures."

Don’t know where to start? The National Park Service has launched the Find Your Park centennial project to help you find a park where you live.

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