The National Park Service is granting free entry today to all sites that usually charge a fee.

GUIDE: National park sites in the tri-state area

It's in honor of National Public Lands Day, which is held annually on the fourth Saturday in September.

While admission is free, you will still have to pay amenity and user fees. 

NPS says National Public Lands Day is one of the nation's largest single-day volunteer efforts. It's meant to celebrate people and the green spaces in their community.

For more information, click here.