For four days in April, national parks across the country will be free to visit.

The free entry days are part of National Park Week, which runs from April 15-23. The free days will be on April 15-16 and 22-23.

On those days, entry fees will be waived to Crater Lake and Lewis and Clark National Historical Park in Oregon. In Washington, they’ll be waived at Mount Rainier, Olympic and Fort Vancouver National Historic Site.

If you want to be a little more adventurous and take a road trip, parks like Yellowstone will also be free to enter on those weekends.

Last year, Oregon saw a record number of visitors at national parks and state parks.

For more information about National Park Week, visit here.