Wednesday, an announcement was made by the The
National Park Service, which runs the parks and monuments across the
U.S., on how they will not be charging any fees for 17 days this year
on all of its country's 394 parks.

The first free day will be held on Martin Luther King,
Jr. Day, Monday, Jan. 17th. Other fee-free days include National Park
Week from April 16th-24th,  the first day of summer, June 21st,
National Public Lands Day, which takes place on Sept. 24th, and
Veteran's Day Weekend ( Nov. 11th-13th).

Source: Reuters