(creative commons/Be The Change Inc.)

Sept. 24 is National Public Lands Day and to celebrate, all National Parks in the United States are offering free entry!

That's right; you have no excuse to stay indoors this weekend.

National Public Lands Day (NPLD) is the country's largest single-day effort to spruce up parks and other open spaces. The event aims the keep the promise of the Civilian Conservation Corps, the tree army that worked from 1933-1942 to preserve and protect America's natural heritage.

More than 180,000 volunteers are expected at more than 2,000 sites across the country and in U.S. territories on Saturday.

The event began in 1994 with three sites and 700 volunteers. It became a huge success and since the first NPLD, the event has grown dramatically. Last year, NPLD volunteers removed an estimated 450 tons of trash, collected an estimated 20,000 pounds of invasive plants, built and maintained an estimated 1,320 miles of trails, planted an estimated 100,000 trees, and contributed an estimated $15 million to improve public lands across the country!

Visit the National Public Lands Day Web site to find a location near you.

While planting trees, repairing trails and enhancing native habitats on NPLD, don't forget to bring your camera. REI is sponsoring the 11th annual NPLD Volunteers in Action Photo Contest. Entrants may have their work featured on the company's Web site in promotional material and the winner will receive an outdoor camping package complete with backpack, sleeping bag, and tent worth approximately $600.

This is the second-to-last free event in the parks for the 2011 calendar year. The last opportunity will come on Veterans Day Weekend from Nov. 11-13.

To find a National Park in your area, visit

Saturday is also Worldwide Day of Play, a flagship event hosted by the National Park Service, the National Park Foundation, and Nickelodeon. The celebration will take place in Washington, D.C. at President's Park.

Hosted by the best in professional and youth sports, health and wellness, and community partners, the event will also bring together stars from iCarly, Victorious, Big Time Rush, Bucket & Skinner's Epic Adventures, Supah Ninjas, True Jackson, and more. Big Time Rush and the Fresh Beat Band will perform live.

Worldwide Day of Play is about getting kids outside and staying active. Nickelodeon will actually go dark all afternoon with no shows on air to encourage parents to get their kids outside.

While the main events are being held in Washington D.C., there are several satellite events across the country.