Will 2016 be the year you embrace—or revive?—your outdoorsy side? Thanks to the National Park Service, it could be, and on the cheap, too. In 2016, each of our 409 national parks will celebrate 16 days of waived entrance fees (and some parks will offer even more!). It’s a fine way to celebrate the 100th birthday of the National Park Service.

According to NPS spokesman Jeffrey Olson, the tradition of fee-free days was formalized in 2009 by then-Secretary of the Interior Ken Salazar. Gratis admission was intended “to give people a break during the depths of the recession,” says Olson, in addition to introducing people to the glory of our national parks.

Here are the 16 fee-free days for 2016, which include a full nine-day stretch this spring:

January 18: Martin Luther King Jr. Day

Martin Luther King Jr. Day April 16 through 24: National Park Week

National Park Week August 25 through 28: National Park Service Birthday

National Park Service Birthday September 24: National Public Lands Day

National Public Lands Day November 11: Veterans Day

According to the NPS site, “the fee waiver includes entrance fees, commercial tour fees, and transportation entrance fees. Other fees such as reservation, camping, tours, concession and fees collected by third parties are not included unless stated otherwise.”

So find your closest park here, and ponder which gorgeous spot to visit here. Fun facts to ponder during your ramble:

April 16th—just after you’ve filed your taxes, natch—is National Park Week every year, and it’s always free.

Fourth graders and their families have free access to every park in America for a full year, thanks to President Obama’s “Every Kid in a Park” initiative.

August 25th will mark the 100th anniversary of President Wilson signing the “Organic Act,” creating the National Park Service.

There were only 35 national parks at that time! Today there are 409.

Why offer so many fee-free days? As Olson says, “we’re trying to touch everybody we can who hasn’t been to a national park yet, to let them know these are great places.”