U.S. National Park Week: Free Admission
On April 19th and 20th you can visit ALL U.S. National Parks and the entrance fee will be waived because it is National Park Week!
According to the U.S. National Park Service, only 133 of the 401 parks charge an entrance fee but during the two days you will be given free admission. However, the NPS wants to remind you that other fees such as reservation, camping, tours, concession and fees collected by third parties are not free during April 19-20th unless noted otherwise by the local park.