Looking for something to do this weekend that's both outdoorsy and free? To kick off National Park Week, you can visit any one of the National Park Service's more than 400 parks on April 21, 2018 for free.

While the majority of the NPS's parks are free year-round, they'll be waiving admission fees to the more than 100 parks that normally require an entrance fee. Which means that you can pay a visit to the Grand Canyon, Death Valley, Yosemite, or Yellowstone National Parks without reaching for your wallet. The timing couldn't be better, as many of the country's most popular parks will be increasing their entrance fees beginning in June.

The National Park Service, which celebrated its 100th birthday in 2016, maintains 417 designated NPS areas that span more than 84 million acres across every state, plus Washington, D.C., American Samoa, Guam, Puerto Rico, and the Virgin Islands.