(CNN) — It's officially autumn, and the US National Park Service has a great way for people to celebrate the equinox this week and a return to cooler weather.
September 24 marks another free entry day to all National Park Service sites that usually charge an entrance fee.
It was established in 1994 and held annually on the fourth Saturday in September. The NPS says the day "is traditionally the nation's largest single-day volunteer effort."
So what's free?
Sunset at Arches National Park, Utah. Normally $30 per vehicle, the park has free entry on Saturday.
All entrance fees. That includes not only those marquee national parks such as Great Smoky Mountains, Yellowstone and Yosemite, but all other types of sites the NPS manages:
Click here for a full listing of every NPS site, which it calls "units."
One catch: "The entrance fee waiver for fee-free days does not cover amenity or user fees for activities such as camping, boat launches, transportation or special tours," the NPS says.
Planning pays off
If you don't like crowds, consider sites with fewer visitors, such as Congaree National Park in South Carolina.
If you're not much of a planner, it might be a good idea to develop the habit -- particularly if you want to see a popular NPS site on a free day.
If you have a particular site you wish to visit, check its website first. For instance, some major roads were closed recently in Death Valley National Park (yes, desert regions can get flood damage, too).
Missed out on this free day? There's one more left in 2022: Friday, November 11 (Veterans Day).