Hoping to check out Rocky Mountain National Park in the fall? Saturday is the day to do it. All national parks are free Saturday in honor of National Public Lands Day. The annual event, which was established in 1994 and, as such, is celebrating its 25th anniversary, is a volunteering day that takes place every fourth Saturday in September, according to the National Park Service. Related Articles Celebrating Ken Burn’s brand of history so that the past may live Guest Commentary: Three weeks remain for Congress to do the right thing for conservation Western business owners throw support behind reauthorizing Land and Water Conservation Fund Solar array on Trail Ridge designed for Rocky Mountain National Park’s extreme weather Writers on the Range: Corporate interests compromise the Interior Department If you choose to take part in a volunteer project Saturday, you will get a coupon for a fee-free day in the future, according to NPS.