There are plenty of reasons to visit one of the many national parks in the U.S., and this weekend, the National Park Service (NPS) is giving adventurers one more. As Travel + Leisure reports, all national parks and sites in the system, from Acadia to Zion National Park, will offer free admission on Saturday, April 20.

National parks are waiving their entrance fees in honor of National Park Week, which runs from April 20 to 28 this year. While many parks are already free to visitors, some national parks, including Yellowstone and Yosemite, cost up to $35 to enter. The free national park day is a great opportunity to visit one of these pricier parks, or to seek out a lesser-known site in your region. (The Find Your Park tool from the NPS can help with that.)

Fees are waived for Saturday, but special activities will continue until Sunday of the following week. At Arches National Park in Utah, for example, guests can participate in painting classes with an artist, and at Gateway National Recreation Area in New York and New Jersey, visitors can learn how to pitch a tent. There will also be themed days throughout National Park Week, like Throwback Thursday, which will highlight the parks system's history, and BARK Ranger Day, when guests can learn about the parks's canine employees.

[h/t Travel + Leisure]