Visitors to Yellowstone and Grand Teton national parks can get in free on Sunday, Aug. 25 in celebration of the 97th anniversary of the National Park Service.

In fact, all 401 national park units will waive entrance fees Aug. 25. The fee for a private, non-commercial vehicle to Grand Teton and Yellowstone national parks normally costs $25 for seven days.

To help celebrate the day in Grand Teton, Park Service “birthday cake” will be served at noon in each of the park’s visitor centers, according to a statement released by the park’s public affairs office.

Visitors can sample cake at the Laurance S. Rockefeller Center, Craig Thomas Discovery and Visitor Center, Jenny Lake Visitor Center and Colter Bay Visitor Center.

A traditional guitar sing-along and evening program will take place at 8:30 p.m. at the Colter Bay amphitheater. The free public program is titled, “For Future Generations: The story of America’s National Parks.”

Also in recognition of the anniversary, the Grand Teton Association is offering 20% off all items sold at bookstores located in park visitor centers.

Visitors are reminded that the fee waiver applies to entrance fees only and does not affect use fees for camping or boating.

For more information on fee-free opportunities in national park units around the country, visit www.nps.gov/findapark/feefreeparks.htm.

In addition to the August 25th fee waiver, America’s national parks will also allow free entry on September 28 (National Public Lands Day) and November 9-11 (Veteran’s Day Weekend).