The National Park Service is honoring its centennial birthday in many ways this year. 

Earlier this week they celebrated with a party at the Brooklyn Bridge Park, and later this week they'll be going even bigger.

From August 25th to the 28th, all 412 national parks in the United States will have free entry.

Think big or think small, day-trip or cross-country―every national park will be at your service.

At the time that President Woodrow Wilson created the National Park Service in 1916, the country only had 35 parks. The founding of the NPS has expanded the nation to a now whopping 412 parks that cover over 84 million acres across all 50 states.

Not to mention the District of Columbia, Puerto Rico, Guam, American Samoa, Saipan, and the Virgin Islands.

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Parks will also be hosting special events including baseball games, choir performances, and cultural festivals. 

Other than these special few days, there are some other chances to enjoy free park admission and events. You can also go for free on September 24th (National Public Lands Day), November 11th (Veterans Day), Martin Luther King, Jr. Day in January, and National Parks Week in April.

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An added bonus: every fourth grader in the country can receive a free national parks pass that works for the whole family for an entire year. Your friends' little siblings have never been more useful.

That’s it, you’re officially out of excuses to enjoy the great outdoors. Get to it, lazies.