Though some national parks, monuments, and other sites are free to explore any day, 108 areas overseen by the National Park Service charge an entrance fee. This includes many of the most well-known ones, like Yellowstone National Park and Grand Canyon National Park.

But on several important days each year, the National Park Service waives those fees. Two of them—Martin Luther King Jr.’s birthday and Veterans Day—are broader holidays, while the other four specifically relate to the great outdoors: the first day of National Park Week; the anniversary of the Great American Outdoors Act; the National Park Service’s birthday; and National Public Lands Day. As Condé Nast Traveler reports, the anniversary of the Great American Outdoors is the only new addition to the list for 2021. Enacted on August 4, 2020, the law allotted as much as $1.9 billion per year (for five years) for the conservation and maintenance of protected lands, and it’s also meant to permanently finance the Land and Water Conservation Fund.

Fee-Free Days for 2021

January 18 // Birthday of Martin Luther King, Jr.
April 17 // First day of National Park Week
August 4 // First anniversary of the Great American Outdoors Act
August 25 // Birthday of the National Park Service
September 25 // National Public Lands Day
November 11 // Veterans Day

If you’re planning multiple park visits throughout the year, you might want to spring for an annual pass, which costs $80 and grants you access to all National Park Service lands. Some people are eligible to claim an annual pass for free; including active military members, military veterans, Gold Star families, U.S. citizens with permanent disabilities; and fourth-grade students. You can learn more about the programs here.

[h/t Condé Nast Traveler]