There are 5 days in 2019 that you are able to visit specific National Parks, and it will not cost you a thing to get in.
The National Park Service says they have set their fee-free days for the 115 of 418 parks that regularly charge, including Acadia National Park in Maine.
Jan. 21: Birthday of Martin Luther King, Jr.
April 20: First day of National Park Week
Aug. 25: National Park Service Birthday
Sept. 28: National Public Lands Day
Nov. 11: Veterans Day.